and the adults of the first generation.

As has been shown, the average period of oviposition among hibernated females is in some cases fully 3 months, while it averages 48 days. The length of the full life cycle for the first generation, as shown in Table XIX, is 24 days, and as the time for the second generation would be slightly less, it is evident that the first eggs for the third generation will be deposited at the same time as those for the middle of the second generation, and also with the very last of the eggs deposited by hibernated females for the first generation. The great overlapping of generations thus produced prohibits the application of any of the common methods of ascertaining their limits. The complexity indicated for the first three generations becomes still further increased as the season advances, so that in October, for example, a weevil taken in the field might possibly belong to any one of six generations. Length of life and the period of reproductive activity are important factors in determining the average number of generations. Periods of greatest abundance can not be regarded as giving any reliable information upon this point, since the number of weevils developed soon comes to depend largely upon the supply of squares.

In the case of the boll weevil, therefore, the information upon the number of generations must be drawn from laboratory sources. Many of the hibernated weevils continue to deposit eggs until the middle of July, and some are active for fully a month longer. In 1903 the last eggs from hibernated weevils were deposited on August 27. In the course of breeding experiments made in 1902 it was found that many weevils which had become adult about the 1st of August would continue to deposit eggs until the latter part of November. Considering the longest-lived weevils and their last-laid eggs, therefore, it is easily possible for two generations to span the entire year. The weevils developing after the middle of November may go into hibernation, and from their last-deposited eggs produce weevils whose last offspring will be ready for successful hibernation again. This conclusion is based upon actual demonstration.

The maximum number of generations will be found by taking the first, instead of the last, deposited eggs in each case. Rather than lay the conclusions open to question by taking the figures found for occasional minimum length of the life cycle, we will take the 24-day period, which has been shown to be the average between June 4 and November 16. Without doubt hibernated females begin their reproductive activity in average seasons by May 1, and their descendants continue to develop normally until after November 15. Taking the dates mentioned, however, as the average season for the weevils, we find that eight generations, each having the average period of development, may usually be produced within the year.

In determining the average number of generations one-third the average period of oviposition should be added to the average life cycle

for each generation." As it has been found that the average period of oviposition is about 5 days, we must allow 24 days for the development of the average adult and 18 more days for the female to deposit one-half her eggs. Forty-two days is therefore about the average length of a generation; and we may thus count on an average of about five generations between May 1 and December 1. In the northern part of the weevil territory, where the season is shorter and the prevailing temperature lower, probably only four generations would be developed.

There is no basis for the idea that there is a distinct hibernation brood. The activity of the adults and the development of the immature stages is gradually retarded by the decline in temperature until hibernation time arrives. Most of the weevils of the first two or three generations have probably died, or then do so, while most of the adults of later generations, having still considerable vitality, will go into hibernation. It is certain that every generation preceding may have some direct part in the production of weevils which shall hibernate. All weevils which are still strong and healthy when cold weather comes on may be expected to go into hibernation, so that there can be no special brood for this purpose.

THERMAL INFLUENCE UPON ACTIVITY AND DEVELOPMENT.

The influence of temperature has been frequently mentioned as an important point, but it may be more clearly understood by collecting some of the most important observations relating to it. A study of this subject throws much light upon such questions as seasonal and daily activity, the rapidity of development at various seasons, hibernation, and the time of emergence from hibernation. The influence upon development will be first considered.

a One-third is nearer the correct fraction than one-half, since it has been found that weevils deposit considerably more than one-half of their eggs during the first half of their oviposition period.

In studying the influence of temperature on development the figures upon the separate stages serve best, as they give the widest range. In each stage it may be seen that the maximum time is nearly, if not quite, four times the minimum, while the average effective temperature difference is in the inverse order, but about 2 to 1. In comparing the minimum and maximum total effective temperatures, it appears that when the average temperature is lowest the total heat required to complete the development of the stage is nearly twice as great as when the average temperature is highest. The length of the developmental period is therefore not exactly inversely proportional to the change in temperature. The retarding influence of decreasing temperature appears to affect each of the immature stages in very nearly the same degree. The total effective temperature required forms a specific constant, which is fairly uniform for average effective temperatures of between 30° and 40° F. These temperatures would, during most seasons, prevail from June to October, inclusive. As the average effective temperature falls below 25° F., however, there results a great and disproportionate retardation in the development. The reason for this difference may lie in the fact that when tempera

ture is ascending from 32° F. it must attain a higher point to start weevils into activity than that at which the same weevil will cease activity when the mercury is going down.

The observations upon the length of the entire developmental period were made upon a different series of weevils. As is clearly shown in the summary given in the latter part of the table, the sum of the average lengths of the three stages agrees remarkably closely with the length of the entire period as found in the 752 cases observed. This close agreement, reached by entirely different methods, indicates that the series from which the averages are obtained are sufficiently large to give constant results, and therefore that the average period of development throughout the season of weevil activity is very close to 18 days.

This thermal influence upon activity in feeding and oviposition may be shown by taking various lots of weevils at intervals through the season. For this purpose the work of 10 males and 10 females has been selected, using the laboratory records for each lot. The time. covered is 25 days in each case to secure a fair average, and 25-day intervals separate the lots from each other. The season thus covered begins with June 6 and ends with November 28, 1903. To make the comparison fair, average conditions as to sex, age, and individual activity must be established, and the records have been selected with these conditions in view.

TABLE XXI.-Thermal influence on activity in feeding and ovipositing.

The average number of daily feeding punctures is reckoned for both sexes alike. Though the females made more than half, the proportions can not be positively separated, and it would make no difference if we could do so. It is noticeable that the period of greatest activity comes in midsummer, with the first, second, and third generations actively at work. Hibernated weevils working in June show greater activity than do the mixed generations which occur together in September and October, though the temperature does not greatly vary. In November, with a marked fall in temperature, there is a corresponding decrease in work, but especially is this noticeable in egg deposition. It appears that at this season and later on the weevils are mostly eating to live until it becomes cold enough for them to hibernate.

LABORATORY EXPERIMENT IN EFFECT OF TEMPERATURE UPON LOCOMOTIVE ACTIVITY.

The experiments here given were performed by Dr. A. W. Morrill. In the absence of apparatus especially designed for such work, use was made of a very simple device, constructed as follows:

A thermometer was passed through a cork and inclosed in a test tube, which in turn was placed within a hydrometer cylinder of sufficient depth to inclose it (Pl. XIII, fig. 49).

Weevils were inclosed in the test tube with the thermometer, and the temperature of the cylinder varied either by heating gently or by the use of ice water. Starting with the thermometer at 64° F., the 10 weevils inclosed were found to move slowly, half of them being quiet. As the temperature was gradually raised the activity of the weevils increased up to 105° F. When the temperature reached 95° F., or over, the weevils were running up and down the tube. By filling the cylinder with cold water the temperature was lowered to 86° F., at which point the weevils began to cluster at the top on the cork and were crawling slowly. By the addition of ice in the cylinder the temperature was lowered to 59° F., at which point 5 weevils were sprawling on the bottom of the test tube or clinging to one another, 4 were clustered on the stopper, while 1 was slowly crawling downward. At 50° F. 6 weevils at the bottom showed slight signs of life and 1 was crawling slowly. At 45.5° F. slight signs of life were still shown, while at 40° F. occasional movements only were noted. Upon the temperature being raised weevils began crawling as 50° F. was passed, and at 64° F. all had left the bottom and were crawling upward. Some recovered much more quickly than did others.

The temperature was again lowered, this time by the use of salt with ice. All movement ceased at 37° F. The cooling, however, was continued to 33° F., after which it was slowly raised to 42° F., at which point movements began.

In a general way these results agree quite closely with outdoor observations.

HIBERNATION.

Even after frosts have blackened the foliage and squares and entirely checked the growth of the plant, some weevils can be found moving in a cotton field upon warm days. Weevils which are old and nearly exhausted die as the cold weather comes on. Their vitality has been expended in other ways and they do not survive the winter. Those which are still vigorous and strong will continue to feed a little, and females will occasionally deposit eggs so long as cotton remains green. In southern Texas larvæ and pupa which are in squares when frost comes are not killed thereby, but slowly finish their development if the weather is warm enough for any activity, and the young adults thus developed may live the winter through without feeding. As