2g The Sexual Organizatiou of the Rhizocephala. 



We have now to describe the manner in which the eggs are passed into the mantle- 

 cavity and the adaptations connected with the process. 



We will take as typical the case of a brood of eggs subsequent to the first in Pelto- 

 gaster. The nauplii of the preceding brood are expelled from the mantle-cavity through the 

 mantle-opening by the rhythmical contractions of the muscular mantle. For some time after 

 the emptying of the mantle-cavity the mantle-opening remains widely gaping, and, by the 

 continued contractions of the mantle, water is pumped in and out of the cavity. After a time. 

 varying according to conditions, as has been previonsly stated, the moult of the mantle externally 

 and of the mantle-cavity internally, together with the plugs of the vasa deferentia, takes place. 

 Immediately after this the sphincter of the mantle-opening becomes tightly shnt but the mantle 

 continues to contract rhythmically and strongly. And now the eggs lying in the greatly 

 distended visceral mass are forced by the muscular contractions of the mantle and of the 

 visceral mass first into the colleteric glands of either side and so into the mantle-cavity. As 

 they pass through the colleteric glands they are surrounded by the slime secreted there. In 

 Sacculina the colleteric glands are greatly branched, each branch corresponding to a diverticulum 

 of the ovary. It thus happens that the eggs of Sacculina are thrust out into the mantle-cavity 

 conglomerated into definite tubiform masses, but the slime which glues the eggs together is 

 glutinous and not solid as Delage supposed. In PeHogaster the colleteric glands being simple 

 the eggs are passed into the mantle-cavity in an irregular mass. 



For at least nine or ten hours the active contractions of the mantle continue in Pelto- 

 gaster (not so actively in Sacculina) , the mantle-opening remaining tightly shut. In this period 

 the processes of maturation and fertilization are completed and the segmentation stages are 

 initiated, and gradually the slime surrounding the eggs begins to solidify attaching them to the 

 lining of the mantle-cavity, a process which is further secured in Sacculina by means of the 

 retinacula. When this process is complete the mantle-opening relaxes and the muscular con- 

 tractions of the mantle quiet down into the slow rhythmical pumping action which serves for 

 the aeration of the developing embryos in the mantle-cavity. 



As to the manner in which the spermatozoa pass down the vas deferens into the mantle- 

 cavity I imagine that this is accomplished by the active vibratile movements of which they 

 are capable; but they may also be assisted by the muscular contractions of the body. They 

 never appear to reach the mantle-cavity until the eggs have been there for some hours; when 

 they do reach the eggs the sphincter of the mantle-opening is of course tightly shut so that 

 eggs and spermatozoa are shaken up together by the contractions of the mantle in a completely 

 closed cavity. 



In ali these facts, together with the fact of the production of ripe sperm only at the 

 period immediately before the maturation of the eggs, we see a series of adaptations, which 

 both for the first and for ali the succeeding batches of eggs are intended to ensure self-fertili- 

 zation with the greatest amount of economy and efficacy. 



