LEPTOTHECA FROM THE MACKEREL 243 



fish both in England and on the Continent, barbel, 

 trout and carp being more especially its victims. 



The genus Leptotheca (Fig. 43), like most of these 

 organisms, shows great polymorphism in its tropho- 

 zoites. The most characteristic appearance of them 

 occurs during movement, when a number of long, 

 narrow, filamentous pseudopodia ,are given off 

 (Fig. 43, A, ps.) and trail usually behind the greater 

 part of the body mass. The main cytoplasmic 

 structure is more or less conical, and when fresh 

 material is examined, the protoplasm appears filled 

 with shining yellowish droplets, probably produced 

 from the bile absorbed by them, for Leptotheca lives 

 in the gall-bladder of certain fishes. During early 

 growth, two nuclei are present, but ultimately ten 

 are formed, five being utilized for each of the two 

 spores produced (Fig. 43, A, sp.). The spores of 

 Leptotheca (Fig. 43, B) are broader than they are 

 long, being 5 to 6 //- long and 6 to 7 //, broad. The 

 mode of transmission of the parasite from one host 

 to another was unknown till recently, but the present 

 authors have established that the method of infection 

 is contaminative. A species of Leptotheca was ob- 

 served by us from the gall-bladder of the mackerel. 

 The spores of this parasite have been traced 

 through the alimentary canal and into the faeces, 

 which, when voided, contaminate the water and thus 

 are so situated as to be readily absorbed by other 

 fish, especially as they swim in schools. 



The genus Ceratomyxa is also a parasite of marine 

 fishes. It is remarkable for its polymorphism. The 

 species that we have investigated from the bile of the 



