2Q The Sexual Organization of the Rhizocephala. 



for this first batch, some other method of fertilization must occur. This other method of 

 fertilization Delage supposed to be derived from the complemental males. 



These complemental males, which to ali appearances are identical with the ordinary 

 Cypris larvae of Sacculina, were found by Delage to be almost invariably present, in numbers 

 varying from two to fourteen, fixed round the mantle-opening of very young Sacculinae which. 

 had only just become external. They were never found at subsequent stages of the growth of 

 Sacculina; Delage therefore concluded that their function was to fertilize the first batch of 

 eggs. This batch, of eggs is, in the species studied by Delage, not mature until about a month 

 after the fixation of the Cypris larvae round the mantle opening; these larvae must therefore 

 in Delage's opinion, either go through some transformation inside the mantle cavity of the 

 Sacculina, or else deposit their spermatozoa in the mantle cavity to wait for the maturation of the 

 eggs. Neither Fritz Muller nor Delage ever succeeded in seeing more than the dead external 

 cuticle of these so-called larvai males, so that the manner of fertilization, if it occurs, is 

 really involved in mystery. 



Now with regard to the ordinary fertilization of the succeeding broods in Sacculina it 

 is not easy to be certain from Delage's account, for although there is nothing to prevent the 

 spermatozoa from escaping from the testes into the mantle cavity, it is difficult to see how they 

 reach the eggs, because the latter, according to Delage, as they pass through the oviducts 

 are surrounded by a solid chitinous investment which would effectually prevent the spermatozoa 

 from reaching them. Delage supposes therefore that fertilization takes place either in the ovary 

 or oviduct, but exactly how this occurs has never been observed. 



The answer to these questions which will be supported in the following pages is shortly 

 as follows. The presence of Cypris larvae, from one to nineteen in number, fixed round the 

 mantle opening of quite young Sacculinae externae (see Piate 6 fig. 1 1) has been found by 

 me, as by Delage, to be almost invariable. In the Sacculina of Inachus scorpio I have cal- 

 culated that they were present in varying numbers in about ninety per cent of the several 

 hundred young Sacculinae examined by me. 



The idea, brought forward by Giard (7), therefore, that their presence is purely acci- 

 dental cannot be accepted, and in view of the common occurrence of complemental males in 

 certain genera of Cirripedes in an exactly analogous position, namely at the mantle opening, 

 I can hardly question that their interpretation by Muller and Delage as complemental males is 

 correct. Now with regard to their function. After studying these larvae in numerous instances, 

 both living and immediately after death, I have determined that they never produce sperma- 

 tozoa, that their cell-contents are doomed to degeneration, and never enter the mantle cavity 

 of the Sacculina, and that the fertilization of the first batch of eggs is effected by the sper- 

 matozoa of the hermaphrodite itself, as in ali succeeding broods. 



For the fertilization of the first batch of eggs both in Sacculina and Peltogaster there 

 is always a passage left free for the escape of the spermatozoa into the mantle cavity, and 

 furthermore Delage was mistaken in regarding the investment of the eggs. derived from the 



