IMPLANTATION OF THE GLOCHIDIUM ON THE FISH 13 



secure. Often, however, they become bent outward along the 

 surface of the fin (fig. 12). 



As Faussek (3) observed and described fully, the fish's 

 tissue which is enclosed within the mantle cavity of the glochi- 

 dium disintergrates and is taken up by the cells of the larval 

 mantle and used as food during the early stages of the para- 

 sitic life. Fig. 12 shows a cross-section through a glochidium in 

 which the mantle cells are sending out pseudopodial processes, 

 and within these cells are numerous leucocytes and fragments 

 of the fish's cells sometimes enclosed in large vacuoles. Harms 

 (10), in describing the way in which these processes arise, states 

 that as soon as the glochidium becomes attached to the fish 

 all the larval tissues begin to grow actively and press on the 

 mantle so that these cells are pushed out into the mantle 

 cavity. Later, as the edges of the permanent mantle are formed 

 along the borders of the shell, the large cells of the embryonic 

 mantle become pressed together more colsely and pushed 

 further into the mantle cavity forming the fungus-like bodies 

 first described by Braun (1). 



The time required for the glochidium to become entirely 

 covered on the fin varies from six to twenty-four hours. Figs. 

 12 and 13 both show cross-sections of glochidia which have 

 been attached to the same fin for six hours. In fig. 12 the 

 epithelium covers only about half of the glochidium, while 

 in fig. 13 it has grown over the entire glochidium, completely 

 embedding it. 



The cysts formed on the fins and on the gill-arches are 

 always much thicker than those on the gill-filaments. This is 

 evident from a comparison of the drawings of cross-sections of 

 glochidia which are entirely embedded on gills and fins, as figs. 

 5 and 14. The tissue of the cyst on the fin never assumes the 

 compact dense appearance with flattened cells closely pressed 

 against the shell, which is characteristic in cysts on the gills. 

 This is evident from an examination of fig. 14, which is a 

 cross-section of a glochidium which has been attached to the 

 fin for forty-eight hours. 



