E. MAKSHALLT. — THESOCYTES. 175 



ing themselves and becoming dispersed from the congi'egated 

 state. The groups are evidently not the resnlt of the coming 

 together of the thesocytes from neighboring parts, for I have been 

 able to trace l)ack their origin to certain archa?ocyte congeries 

 described in the last chapter. T!ie archa>ocytes develop into the 

 thesocytes by gradually accumulating the fat-like bodies in the 

 protoplasm, whereby the cells grow considerably in size. PI. IV, 

 fio-. 24 illustrates the transition of a mass of archoeocvtes into 

 that of thesocytes. On the left of that figure are seen a number 

 of archfeocytes still in the original state ; toward the right they pass 

 into thesocytes by an uninterrupted series of intermediate stages. 



As before mentioned, the orange-yellow spots, i.e., the 

 thesocyte-masses, are very variable in size. Some are quite 

 minute, while others may be as large as half a millimeter across. 

 This indicates that the transformation into thesocytes may take 

 place at any stage in the growth of archasocyte congeries. It is 

 probable that even a solitary archseocyte may develop into a 

 thesocyte ; but of this I liave no direct evidence. The thesocyte- 

 masses were not noticed by me in any other species tlian in 

 E. marshalli, and it may be necessary in the former cases to 

 assume that the thesocytes there present in scattered distribution 

 arise from similarly circumstanced archa?ocyets. 



The question, whether all the archoeocyte congeries in E. 

 marshalli are destined to undergo tlie above develoiiment, is, I 

 believe, to be answered decidedly in tlie negative. (See ante, 

 p. 172, & anon under Reproductive Elements). AVhile the 

 process is to be called perfectly normal, it appears to represent 

 a special case of the functional and morphological differentiation 

 of archajocytes, taking place under certain physiological condi- 

 tions, which are difficult to determine but which at all events 



