168 MEDICAL ZOOLOGY. 



canal, which is expanded at its lower portion, finally to open near the inferior 

 margin of the ventral sucker ; eggs pointed at one end. (Cobbold.) 



Habitat. Egypt: man and monkey. Found in the blood-vessels; the 

 eggs may act as thrombi, yet no pyemic symptoms are seen. 



Tetrastoma. T. renale, Delia Chiaje. This imperfectly known parasite 

 possesses an oval flattened body, 5"' long, having 4 suckers at caudal end. 

 Habitat. Kidney ; very rare ; only one case recorded. 



Hexathyridium. Body oblong or lanceolate. Head continuous with the 

 body. Mouth placed anteriorly, subterminal. Suckers six, behind the vari- 

 olar margin. Genital pores of the body, ventral, approximate, superposed, 

 the larger in form of a sucker. (Diesing.) 



H. pinguicola, Treutler. Body oblong, convex above, concave beneath, 

 acuminate anteriorly, truncated posteriorly. Suckers six in number, ar- 

 ranged in the form of a semicircle at base. Genital pores near one another 

 in the neighborhood of the greater sucker. 



Measurements. 8'" long ; 3'" wide. 



Habitat. Ovary of human subject ; rare. 



H. venarum, Treutler. Body obtuse, lanceolate. Suckers arranged in 

 two longitudinal rows. 



Measurements. 2-3'" long; -2'" wide. 



Habitat. Sputa of haemoptysis and blood from tibial vein. 



DEVELOPMENT OP TREMATODA. 



The impregnated egg of Fasciola and Distoma hepatica undergoes com- 

 plete (?) segmentation. The embryo escapes as an oblong, ciliated planula. 

 The subsequent stages of development have not been traced in the species 

 found in human subject, but in other Trematoda as, for example, the 

 species of Distoma infesting an aquatic snail (Limnceus stagnates) the de- 

 velopment has been carefully studied, and it is reasonable to suppose that it 

 is not materially different from that of the other species. The interior of the 

 planula produces independent larval forms, probably by a process analogous 

 to that witnessed in Aphis. But the larvae, instead of at once escaping, re- 

 main within the parent larva case (Konig's gelbliche Wurm), as in Cecido- 

 myia. This enclosed brood, as it may be termed, escaping, have evolved from 

 within their bodies a second larval brood (Cercarice). Each zooid possesses 

 peculiar Distoma-\ikQ features, viz., two suckers and an intestinal tube bifur- 

 cating in advance of a ventral sucker, but differs from Distoma in the pos- 

 session of a row of hooks about the position of mouth, in the presence of a 

 long natatory tail, as well as in the absence of organs of generation. The 

 cercarial larvae in their turn escape from their encasement, and swimming 

 freely about, attach themselves to the integument of the snail to be infested, 

 and endeavor, by their hooks, to effect an entrance into its tissues. This 



