94 The Sexual Organization of the Rhizocephala. 



of hypertrophied degeneration. In this manner only a very small quantity of spermatozoa 

 are produced at a time. This is also the case in ali the closely allied genera, e. g. Parthenopea, 

 Lernaeodiscus and Heterosaccns. 



The only genus in which this is not the case is Clistosacciis , where the whole length 

 of the single testis may produce spermatozoa, and where no signs of hypertrophied degeneration 

 are visible, the whole length of the testes having the appearance shown in figures 8 and 9 

 Piate 8. It is possible here that a compensation has been brought about by the development 

 of only a single testis. I must admit however that the single testis of this animai produces 

 more sperm than the two testes in any other species. 



Another connected feature in the spermatogenesis of the Rhizocephala is its strictly 

 rhythmical nature, so that ripe spermatozoa are never to be found in the testes except immedia- 

 tely before the ova of the various batches are ready to be fertilized. 



Furthermore, at any rate in Sacculina, it appears that only one testis usually functions 

 at a time, i. e. contains ripe spermatozoa, an observation originally made by Delage, and con- 

 nrmed by Duboscq and myself. 



In ali these means for securing an economy in the production of spermatozoa we see 

 an adaptation incident on self-fertilization. If we compare the Rhizocephala in this respect 

 with other Cirripedes in which the hermaphrodites habitually cross-fertilize one another, it is 

 at once apparent that in the latter an immensely greater mass of spermatozoa is produced, 

 and that none of the germinai cells undergo the hypertrophied degeneration which renders 

 sterile the greater number of the cells of the testis in the Rhizocephala: and this is ali the 

 more striking because in the production of eggs the Rhizocephala are far more proliflc than 

 any other Cirripedia. But since their eggs are fertilized, as we shall see, by the sperm of 

 the same individuai which produces them, there is no possibility of a loss of spermatozoa 

 through the accidents that may accompany cross-fertilization, and in this manner we can under- 

 stand the possibility of this great economy in the production of sperm being practised. 



2. The moulting of the mantle-cavity and of the vas deferens and the 



passage of the ova into the mantle-cavity. 



We have now to explain the manner in which the spermatozoa, when they are mature 

 are brought into contact with the eggs, and fertilization effected. 



The mantle both externally and internally is lined with chitin, and the chitinous in- 

 vestment of the mantle-cavity internally is continued into the lining of the vasa deferentia. 



In Peltogaster when the animai moults the whole chitinous investment of the exterior sur- 

 face of the body, of the interior surface of the mantle-cavity and of the vasa deferentia may 

 be cast off as one continuous sheet at the same time. Often in Peltogaster and probably 



