No. 614] PHYSIOLOGICAL PROBLEMS 



147 



rence of adults, and noting that the species have been ar- 

 ranged in the seasonal order, starting with Pardosa mod- 

 ica Beck, which was taken only in April, we end the 

 season with adult Argiope trifasciata, which appeared as 

 adults late in the season only. 



We note that when the collection proved at all complete 

 the juvenile individuals follow the adults of the early 

 spring species, and that they both precede and follow the 

 species which mature late in the season. The collections 

 proved to have been made with insufficient detail, and 

 many young spiders could be identified only to the genus 

 and are usually omitted entirely. However, the tables 

 show a sufficient general arrangement of the species 

 throughout a season to furnish an adequate basis for a 

 discussion of the problems involved in the phenomenon 

 of seasonal succession— the problems presented by a com- 

 parison of the few species whose life histories are known 

 quite completely. 



IV. Discussion 

 Nearly all species are adjusted to the seasonal rhythm 

 of the habitat in which they live. Thus Dyctina sublata 

 appears as adult in May and June, when, as it seems, eggs 

 must be laid, and juvenile forms characterize the late 

 summer and autumn. Argiope trifasciata deposit eggs in 

 October and passes the winter in the juvenile form. Phi- 

 dippus podagrosus reaches maturity in July, when eggs 

 must be deposited, and young occur in both fall and 

 spring. These differences generally represent an innate 

 adjustment of the life cycle to seasonal rhythm, not read- 

 ily broken up. It is to be expected, then, that Dictyna 

 will deposit eggs to better advantage and that the young 

 hatch better in May than in November, as is the case of 

 Agelena nivea. It is further to be expected that the 

 young stages of some spiders will not go on with develop- 

 ment until cooled for a considerable period. Perhaps one 

 of the most interesting questions concerning the whole 

 matter of succession of spiders is to be found in the fact 

 that from what is known about them, they are all active 



