3. The Endoparasitic development of Peltogaster eocialis, and Polyembryony in Sacculina. 57 



3. The Endoparasitic development of Peltogaster socialis, 

 and Polyembryony in Sacculina. 



It is only possible to touch lightly here on a subject which offers a very interesting 

 field of research, but since the species in question is not at all common at Naples I am only 

 able to give a few notes which may perhaps be of value for the future. 



Peltogaster socialis, a parasite of Eupagurus prideauxii and meticulosus, is remarkable for 

 the fact that it is never found solitary, but always infests a single host in numbers varying 

 between 4 and 30, the usual number being about 20. In Plate 6 fig. 7 I have drawn 

 a specimen of E. prideauxii which carried 22 parasites. The shape of a single animal is 

 shown in fig. 8 ; in anatomical characters it does not differ in any respect from the ordinary 

 solitary kinds of Peltogaster. 



The numerous parasites affixed to each host are always at very much the same stage 

 of development, so that the infection by so many individuals must have taken place at the 

 same time. There is a certain mystery to be solved here, because the parasite in general is 

 so rare that its occurrence, when it does occur, in such large numbers on a single host, must 

 either mean a most peculiar gregarious habit in the Cypris larvae, or else we must look for 

 some quite different explanation. The explanation which occurred to me was that the numerous 

 individuals on a single host are really the product of a single Cypris larva by a process of 

 budding from the endoparasitic central tumour and its root system. Although this would mean 

 an unique process in Crustacea, namely the production of a true colony by budding, there 

 is nothing inherently improbable in the hypothesis, if we take into account the peculiar nature 

 of the development of the Ithizocephala, i. e. the assumption in the middle of the develop- 

 mental history of an embryonic condition. 



There is also a further fact which made me expect to find such a process of budding. 

 Delage in his Memoir makes mention (I p. 665) of finding in the central tumour of a Sac- 

 culina interna two cellular masses, representing the future visceral mass and mantle, instead 

 of one, and he wonders whether it is possible for a single tumour ever to give rise to two 

 Sacculinae; but he dismisses the idea, partly because his preparation was a poor one and 

 partly because the hypothesis is contrary to the general facts of development. 



Now in the course of my investigations on Sacculina interna I have found incon- 

 testable evidence on two occasions that Delage's first opinion is perfectly correct, and that 

 occasionally two Sacculinae may begin to develope from a single central tumour; but whether 

 two such Sacculinae ever come to maturity I am unable to say. One of these specimens is 

 shown in Plate 6 fig. J 0. It is here seen that two mantle and visceral masses are developing 

 opposite one another in a single centra] tumour, which must of course have been produced 

 from a single Cypris larva. 



Zool. Station zn Neapel, Fauna and Flora, Golf von Neapel. Rhizocephala. 8 



