HABITS, ETC., OF CEREBRATULUS LAGTEUS. 115 



In Cerebratulus, on the contrary, the genital elements are 

 distributed throughout the whole body, and if there be any 

 priority in ripening, it is in favour of the anterior and not 

 the posterior portion. Fission does not take place until after 

 the eggs and sperm have been discharged, and hence it 

 cannot be regarded as assisting that discharge in any way. 



We are thus confronted again with the question, what 

 advantage can result to the worm in thus parting company 

 with a large portion of its body at this particular time ? 



The body is composed essentially of two series of pouches, 

 arranged in alternating pairs on either side of the straight 

 intestine. Ordinarily the digestive pouches occupy the larger 

 part of the space, but as the breeding season approaches the 

 reproductive organs begin to enlarge, and by the time the 

 sexual products are ripe they occupy practically the whole of 

 the space, and the intestinal ceeca are flattened between them 

 until their opposite sides meet. This is especially true in 

 the posterior portion of the body, which at this time becomes 

 little more than one large ovary or testis, divided into lobes 

 by the flattened caeca. Mcintosh (34) states that " the 

 glandular elements in the walls of the digestive tract undergo 

 a certain amount of atrophy during the period of reproduc- 

 tive perfection." For a long time, therefore, these intestinal 

 pouches can function very little, if at all, and so they contri- 

 bute nothing to the nourishment of the body. 



After the eggs and sperm have been discharged there is 

 evidently still less use for them until the next breeding 

 season, and regeneration proceeds so fast that before that 

 time a new body will have been formed. In fragmenting, 

 therefore, at the close of the breeding season, it would seem 

 that Cerebratulus is parting company with a portion of its 

 body which has for some time been devoted to a single pur- 

 pose, that of perfecting the sexual products, and of which, 

 now that this purpose has been accomplished, it has no im- 

 mediate need. 



Fragmentation under irritation is evidently a defensive 

 action. As Hubrecht (27) well says^ '^ an animal that at the 



