306 



THE AMEBIC AN NATURALIST [Vol. XL VIII 



6. During the process of regeneration the behavior 

 gradually becomes more responsive and finally is like the 

 normal individual. This appears to be correlated with 

 the growth of a new nervous system. 



7. Thyone is functionally a bilateral animal, but the 

 most conspicuous individual differences involve struc- 

 tures that have <a radial arrangement. 



8. The Polian vesicles vary greatly in number, size 

 and location. There is a strong tendency for these to 

 occur on the left side, and this arrangement is undoubt- 

 edly due to ancestral conditions, for the present bilateral 

 habits of Thyone could probably have no influence in 

 producing this asymmetry. 



9. The retractor muscles in a single radius consist of 

 single or multiple strands, and this variation is closely 

 correlated with a similar variation in the number of 

 Polian vesicles. No explanation is forthcoming for this 

 peculiar plasticity of the retractor muscles, but the sug- 

 gestion is made that it may be functionally correlated 

 with the development of the water-vascular system. 



10. It was found from the study of a number of speci- 

 mens that individual peculiarities of structure tend to be 

 reproduced in the process of regeneration. In this proc 

 ess it would appear that individual variations tend to 

 predominate over generalized ancestral influence. 



11. Autotomy enables Thyone to survive for a consid- 

 erable period on a smaller than normal supply of oxygen. 

 Nevertheless, the conditions which give rise to self-muti- 

 lation are seemingly in all cases pathological. 



12. The conditions in Thyone afford some evidence for 

 believing that when this animal abandoned the fixed stage 

 the Polian vesicles conformed more or less to the radial 

 type. This is opposed to the statement of Lang that in 

 all cases where a multiple number is now present " there 

 was originally only one vesicle." It is believed that the 

 present arrangement of Polian vesicles in Thyone can be 

 best accounted for on the theory of phylogenetic influ- 

 ence. That, in general, those vesicles have retained their 

 most complete radial arrangement in those species of 



