THE WINDOW-PANE OYSTERS. 



47 



Parasitic infection takes place at an early age, as is indicated by 

 the observations recorded under Sambore river, Station VII. A 

 simple larva \vith large granules from the smaller of the two infected 

 specimens is shown in fig. S. The larger (No. 2) had a monogen 

 (fig. 9), the contained endogen undergoing continual movements of 

 contraction and expansion. An older placuna (Sambore river, 

 Station VIII. , No. 1) exhibited many different stages, from the barren 

 microgen to the polygen. The irregular shape of the endogens is a 

 consequence of their soft contractile bodies. 



Fig. 2. — Monogen cyst of intermediate size. The large granules are outside 

 the endogen. Zeiss. 3 C. cam. luc. Tamblegam. 



In fig. 6 the endogen appears like an imaginal disc carved out of 

 the substance of the parent ; in this instance the cluster of small 

 granules had not yet formed, those seen in the sketch being peripheral 

 granules of the parent outside the endogen. Frequently when a 

 single endogen is present it occupies the greater part of the body 

 of the parent, but sometimes the contrast in the size of parent and 

 offspring is very great as will be noticed below. 



In another cyst from the same host (Sambore river, Station VIII., 

 No. 2) seven endogens could be clearly distinguished, and I noted 

 that, as a rule, the endogens were placed peripherally in the cyst, the 

 bulk of the calcareous concretions internally. In this placuna dia- 

 tomaceous ooze was seen adhering to the tip of the crystalline style, 

 indicating the nature of the food upon which placuna subsists. 

 Fig. 7 shows a monogen from the same host, in which the endogen 

 appears with its anterior end retracted, and a pore is visible at the 

 hinder end of the parent. In the preparation from which this was 

 taken about eight larvae were found in the field of the microscope. 



