1908] Biological Notes on Pototo Beetle 171 



very exceptional, according to Tower, for it is implied that he was 

 unable to find such either under a great variety of natural habitats, 

 or under all possible laboratory and experimental conditions. 

 Hence it seems all the more strange that these phenomena 

 should occur from the first under ordinary laboratory conditions, 

 in a breeding experiment which was purely incidental. 



But Tower does not give all of the matter concerning this 

 question together, and it is in the later portion of his work that 

 we find the most pertinent data on it. This is in relation to the 

 production of special races by breeding under controlled condi- 

 tions. 



If a race can be considered the same as its species. Tower prac- 

 tically admits that there may he on occasion, more than two an- 

 nual generations, and thus contradicts himself, for he says on page 

 251: " Closely associated with the hibernation of the second 

 generation in these beetles is the c{uiescent or resting period in 

 the cycle of the germ plasm. That is, the germ cells do not de- 

 velop at all in the autumn, but remain as oocytes or sperma- 

 tocytes, which are relatively few in number, until the following 

 spring after emergence from hibernation, when they develop 

 rapidly. This period of inactivity in the reproductive elements 

 has been regarded as due to some inherent necessity for rest in 

 the germ plasm. However, it does not seem to me to be of this 

 nature; it is rather in the nature of a very deep-seated adaptation, 

 like aestivation, which has been developed and retained not only 

 in this genus, but also in the whole insect phylum, for the pur- 

 pose of enabling them to pass successfully over the season of the 

 year when unfavorable conditions of existence are most apt to 

 occur. In my experiments a race arose suddenly in which there 

 were five generations, and then a period of rest, and then five 

 more, and so on." From this quotation, it is apparent that 

 Tower obtained five seasonal generations with what he calls a 

 race of the species decemlineata. I believe, however, that the 

 distinction is justifiable because the appearance of the individuals 

 with five annual cycles, under controlled conditions in confine- 

 ment, was relatively scarce, abnormal, and they had racial char- 

 acteristics. 



Again, Tower {lb., pp. 280-281) gives another illustration of 

 the occurrence of more than two annual cycles: "A variation 

 which arose from decemlineata obtained at McPherson, Kansas, 

 appeared in my culture in June, 1904. This was rubrivittata. 



