pj4 The Endoparasitic Development of the Rhizocephala. 



2. The Endoparasitic Development of Peltogaster curvatus (Kossmann). 



(Piate 6 figs. 1—6.) 



With the exception of a no^e by Schimkewitsch (2) no account has been given of the 

 internai development of Peltogaster. 



Peltogaster in its endoparasitic development follows an essentially similar course to 

 Sacculina, but with certain very instructive and interesting deviations. Silice this parasite is 

 by no means so frequent as Sacculina, it is difficult to obtain a complete series of stages; I 

 have been so fortunate, however, as to fìnd several specimens at an exceedingly early stage 

 of endoparasitic development, corresponding to that described above for Sacculina under the 

 name of Sacculina interna migrans. 



This stage in Peltogaster is figured in Piate 6 figs. 1, 2 and 3. The long stolon-like 

 structure drawn under a low power in fig. 1 was found in ali cases in the position where 

 the roots of the adult are finally situated, namely clinging to the gonad, or to the liver near 

 the gonad, on the left side of the body. It was situated entirely inside the body of 

 its host with no communication or contact with the external epithelium. 



I may mention here that Mr. F. A. Potts of Trinity Hall, Cambridge, in the course of 

 his investigations on the effect of Peltogaster on Eupagurus meticulosus, has found two specimens 

 of Peltogaster at this early internai stage which he handed over to me for further study. 



The body, which is at this stage of a pale green colour, consists of an elongated hollow 

 centrai tumour which is beginning to throw out slender roots in ali directions. At present 

 no sign of the difFerentiation of the mantle and visceral mass is visible: histologically the 

 centrai tumour is composed of a single epithelial layer of large cells, many of which are 

 undergoing mitosis, and the roots have an identical structure. But at the extreme anterior 

 end (Piate 6 fig. 1 n) in the region where the mantle and visceral mass will soon be difFeren- 

 tiated, the epithelium has given rise to a quantity of smaller cells which lie beneath the sur- 

 face. Fig. 3 is a drawing of a whole preparation of this region. Fig. 3 a is a drawing of a 

 root. In some of the specimens, the roots were short, but in others the growth of the roots 

 had proceeded further and were quite unmistakably identical in structure and appearance with 

 those of an adult Peltogaster, although considerably smaller. It should be observed that the 

 roots of Peltogaster do not branch and subdivide, like those of Sacculina, but continue as long 

 unbranched fìlaments even in the adult. The method of growth of Peltogaster is thus a little 

 difFerent and more simple than that of Sacculina, for whereas in the latter the centrai tumour, 

 as it grows to its definite position, becomes broken up into a multitude of ramifying roots, 

 in Peltogaster the centrai tumour from the earliest period, when roots are being formed, occu- 

 pies pretty accurately its definitive position and from that position sends out simple unbranched 

 roots. In an old Peltogaster the centrai tumour is no longer present as such, having broken 



