IMPLANTATION OF THE GLOCHIDIUM ON THE FISH 3 



hours, but usually about twenty-four hours are required and the 

 cyst continues to grow thicker until the third or fourth day. 



According to Schmidt (15) the epidermal cells of the fish 

 begin to proliferate twenty-four hours after the infection and 

 by the third day the complete cyst is formed. 



Faussek (3, 4) devotes more attention than any previous 

 observer to the changes brought about in the tissues of the 

 fish as a result of the presence of the glochidium. He describes 

 in detail the way in which the larval mantle cells act as an 

 organ for taking up food. The formation of the cyst is regarded 

 by him merely as a process of healing of the wound produced 

 by the parasite. On studying the changes which take place in 

 the cyst after its formation he observed the appearance of 

 intercellular spaces arising in consequence of an accumulation 

 of lymph. 



Harms (7-10) more recently has made a detailed investi- 

 gation of the post-embryonic development of three different 

 species of mussels, and in connection with this work he records 

 a number of observations on the general conditions under 

 which parasitism occurs. Reference will be made further on 

 to such of his results as bear upon my own observations. 



MATERIALS AND METHODS 



The glochidia of Symphynota complanata, Lampsilis 

 ligamentina , Lampsilis recta and of Unio complanatus were 

 used as material for the study of the relation of the parasite 

 to the tissues of the host. 



The first three belong to the group of mussels known as 

 "winter-breeders" in which the glochidia are carried in the 

 gills throughout the fall and winter and are normally discharged 

 during the following spring and early summer. Glochidia are 

 therefore easily obtained during the gravid period of the 

 mussels, and if they are removed from the marsupium at any 

 time during this period and fish infected with them, they will 

 undergo the metamorphosis. This seems to indicate, as Harms 

 (10) suggests, that the retention of the glochidia in the mar- 



