EXPLANATION OF PLATE 2 



All figures were drawn from stained permanent mounts in damar, by the aid 

 of a camera lucida. 



Symbols : c g, cement gland ; g n, giant nucleus of subcuticula ; I, lemni- 

 scus ; n, neck; r, receptacle of proboscis; t, testis. 



Echinorhynchus thecatiis (Linton) 



Fig. I. A young male, showing general arrangement of internal organs. 



Fig. 2. Hard-shelled embryo from body cavity of a gravid female. Three 

 protective membranes of varying thickness surround the group of cells that 

 have been derived from the fertilized egg cell by cleavage. Embryos are dis- 

 charged into the water at this stage. 



Fig. 3. Larval cyst from peritoneum of yellow perch (from Wisconsin). 

 Fishes may serve this parasite as intermediate hosts. If the amphipod which 

 swallows the hard shelled embryo is unmolested the larva attains its full larval 

 development in the primary host. In case a fish devours a primary host 

 containing slightly developed larvae it seems probable that the larvae become 

 encysted in the tissues of the fish, which thereby becomes an intermediate host, 

 sheltering the larvae until they reach the infecting stage. 



Fig. 4. Juvenile form from intestine of fish. This individual is in the same 

 stage of development and is of the same size as the encysted larvae from 

 primary or intermediate hosts. 



Neoechinorhynchus cylindratus (Van Cleave) 

 Fig. 5. Outline drawing showing general body form and the distinctive 



swellings that indicate the location of the giant nuclei of the body wall. 

 Fig. 6. Proboscis, showing typical spheroidal form and the number and 



arrangement of hooks. 



Fig. 7. Embryo from body cavity of gravid female. 



Pomphorhynchus bulbo colli Linkins 



Fig. 8. Young male, showing general arrangement of organs. This species 

 is readily distinguishable by means of the very long neck, which bears an 

 mflated enlargement just behind its attachment to the proboscis. 



Fig. 9. Embryo from body cavity of gravid female. 



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