628 PHOTOPERIODISM IN INVERTEBRATES 



measured as easily as in the echinoderms, in the abalones and 

 lamelHbranchs the gonad is interwoven with the digestive tissue. 

 Therefore, in the abalones the digestive gland-gonad complex was 

 frozen and sectioned, and tracings were made of the areas filled with 

 gonadal tissues of representative sections throughout the gonad. Teased 

 gonads were also examined for eggs and sperm. In the lamelHbranchs 

 the presence of mature eggs and sperm was used as a means of de- 

 lineating the breeding season. Small immature eggs appear in a certain 

 number of animals before the mature eggs show up. In this way the 

 breeding condition can be quantized by counting the number of 

 animals in which sex cells are indistinguishable and giving arbitrary 

 ratings for appearance of immature cells, mature cells in some, mature 

 cells in all, etc. 



In crustaceans the gonadal tissue proved to be impossible to assay 

 quantitatively because of difficulty in removing the delicate tissues 

 intact from the animals. In the male, for example, the seminal vesicle 

 becomes engorged with sperm and is easily torn. Therefore, the 

 breeding condition was determined by counting the number of females 

 carrying eggs as well as the state of development of the eggs. When 

 the majority or all of the females carry eggs and the eggs are in an 

 advanced state of development, the animals are considered to be in 

 the height of the season. 



Initially, twenty animals were sampled twice monthly, but the data 

 were no more informative than data on a sample of ten animals 

 gathered monthly; therefore, the latter sampling method was con- 

 sidered adequate for most purposes. Larger numbers are sampled 

 when feasible. 



Such other data as seemed pertinent were gathered in some cases, 

 e.g., the hepatic index, determined in the same manner as the gonad 

 index in the starfishes and the chitons. Chemical constituents of the 

 gonads and the hepatic glands were determined and will be men- 

 tioned where pertinent in a discussion of the experimental results. 



EXPERIMENTAL 



Examination of Table I discloses that the breeding season is by no 

 means the same for different species of marine animals taken from 



