CALMA GLAUCOIDES 453 



his raft experiment that the life-cycle of such a much less 

 advantageously placed animal as Galvina is far shorter than 

 had been imagined. What must it be then in a case where 

 food is plentiful if found at all, and its nutritive value so great 

 that a hind-gut is useless ; where, moreover, the chemical 

 constitution of the food and the gonad which it nourishes must 

 be so similar as to reduce the entailed metabolic conversion to 

 a minimum ? In fact, such an economical metabolic system is 

 equalled only by parasites that absorb the gonads of their hosts. 

 As to the special cells of the cerata, the supposition that they 

 act as reservoirs of food during a fast is supported by the 

 incidence of their periods of growth and diminution, while the 

 fact that only the connective tissue cells of the cerata are so 

 employed agrees with the principle observed throughout in 

 Calma, namely, that the whole available body-space should be 

 reserved for the alternation of food and gonad. 



General Considerations. 



The Aeolidiomorpha are all carnivorous, and the Aeolididae 

 all eat Coelenterates. The smaller ones live on Hydrozoa, but 

 supplement that diet by eating other members of their own and 

 neighbouring species or their eggs. Such are Facelina and 

 Favorinus, and it was among these most probably that Calma 

 arose, and, in spite of its extensive aberration from type, it 

 is to be hoped that no systematist will think fit to separate it 

 from them. The contours of the body are still typically 

 Aeolidian in detail. Examination of the least plastic of bodily 

 systems, the nervous system, by itself would place Calma in 

 the genus Facelina. During the precarious early days of settling 

 down on the sea bottom it is highly probable that the little 

 animal actually uses its initially uniseriate Aeolidian radula as 

 a generalized carnivore. All the departures from the Aeolididae 

 in the structure of the alimentary and other systems have been 

 shown to be closely associated with the adoption of a diet 

 different from and even more specialized than that of its polyp- 

 eating relatives. In doing this it provides an exception to the 

 rule that, as Dr. Willey expresses it, the adoption of a special- 

 ized diet marks the culmination of a phyletic career. 



