4. The complerueutal males. 3 1 



larvae which are in process of infecting a crab, except that no special chitinous investment 

 is formed round the embryonic cells to produce the Kentrogon stage. 



And now one of two things may happen ; either the antenna splits and the embryonic 

 cells pass out into the pocket round the mantle-opening where they may frequently be found 

 in the act of degeneration, or else they remain in the Cypris body and disintegrate there. 



In only one instance have I observed a case in which the mass of embryonic cells, owing 

 to the antenna of the Cypris being deeply imbedded in the substance of the mantle, had passed 

 within the chitinous plug occluding the mantle-opening and lay in the folds of the mantle 

 round the opening. 



After repeated attempts to hnd any other explanation of the matter, I have unwillingly 

 adopted the conclusion that these Cypris larvae and their contents are in all cases doomed to 

 degeneration and that they no longer play any part in the propagation of their species We 

 may scrutinise the mantle-cavity and mantle and the whole body of Sacculinae between the 

 period of fixation of the Cypris larvae round the mantle-opening and the maturity of the first 

 brood of eggs, a period of about three weeks in Sacculina neglecta, but there is never a trace 

 either of spermatozoa or of the embryonic cells to be found. If those cells really play anv 

 part in furnishing spermatozoa for the fertilization of the first brood of eggs it is inconceivable 

 that one should not be able to detect them somewhere. For they cannot be lying scattered 

 about in the mantle-cavity, since the latter is being continually washed out with water, and 

 moreover when the embryonic cells leave the Cypris larvae, on the occasions when they do 

 succeed in this, they are far from being spermatozoa and would have to go through numerous 

 divisions and changes. Finally we have seen that as a matter of fact the spermatozoa which 

 fertilize the first brood of eggs are derived from the testes of the hermaphrodite, and that 

 when they do reach the mantle-cavity there is not the least difficulty in detecting them. Why 

 then should we suppose that the embryonic cells of the Cypris larvae, which are in so many 

 cases actually seen to degenerate, can give rise to spermatozoa which remain invisible for three 

 weeks and are only to be detected at the moment of fertilization? 



It is my conviction, then, after examining these larvae living and in process of degene- 

 ration on numerous occasions, and after searching in vain for any trace of their products in 

 young Sacculinae between the period of fixation of the so-called complemental males and the 

 fertilization of the eggs of the first brood, that they represent in a certain sense a degenerate 

 sex, but the explanation of their true nature and persistent presence despite their uselessness 

 will be deferred until the end of the chapter. 



B. In Duplorbis calathurae (?). 



(Plate S figs. 14, 18, 19.) 



I have now to describe the remarkable bodies found in the mantle-cavity of Duplorbis 

 calathurae, the species discovered by Dr. H. J. Hansen on the Isopod Calathura brachiata from 

 Greenland. These bodies are of an admittedly problematic nature, since there has been no 



