STRUCTURE OF CLINOSTOMUM 221 



The yolk receptacle lies near the ovary and its duct reaches the 

 oviduct as already noted. The shell gland surrounds the ootype 

 at this point. Its cells radiate from the ootype and their long 

 tapering portions seem to communicate with its cavity, though it 

 is not possible to recognize absolutely the manner of connection. 



The egg. The eggs measure 0.099 mm. by 0.66 mm. There 

 is a distinct operculum very near the end of the shell. The shell 

 in some cases is deeply stained by the haematoxylin and looks as 

 if composed of the same substance as the spines. In other cases 

 the shell is not influenced by the stain. The shells contain as 

 usual a fertilized cell derived from the ovary and several cells 

 derived from the vitellaria. The eggs, both those of the uterus 

 and the older ones of the uterine sack are practically undeveloped. 

 In some cases the true egg cells may undergo one or more of the 

 early stages of cleavage but in the vast majority of eggs no devel- 

 opment takes place during the time that they are lodged within 

 the body of the parent. In view of this we must recognize the 

 sack as merely a place for the storage of eggs. The reason for this 

 storage remains for the present unknown. 



BIBLIOGRAPHY 



Benham, W. B. 1901 A treatise on zoology, edited by E. R. Lankester. Vol, 

 4. The Platyhelmia. 



Bettendorfek, H. 1897 Ueber Musculature und Sinneszellen der Trematoden. 

 Zool. Jhrb., Abt. Anat., Bd. 10, pp. 307-385. 



Blochmann, F. 1896 Die Epithelfrage bei Cestoden und Trematoden. Ham- 

 burg. 



Braun, M. 1893 Bronn, Klassen u. Ordnungen; Platyhelminthes I, Trematoden. 

 Bd. 4, pp. 396-924. 



1900 Die Arten der Gattung Clinostomum Leidy, Zool. Jhrb., Abt. 

 f. Syst., Bd. 19. 



BuGGE, G. 1902 Zur Kentniss des Excretionsgefasssystems der Cestoden und 

 Trematoden. Zool. Jhrb., Anat., Bd. 16. 



Leuckart, R. 1889 Die Parasiten der Menschen, u.s.w. 



Linton, E. R. 1898 Notes on the trematode parasites of fishes. Proc. U. S. 

 Nat. Mus., vol. 10 pp. 507-548. 



1910 The diagnosis of a case of parasitism in the brook trout. Proc. 

 Seventh Internat. Zool. Congress, Boston Meeting, 1907. 



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