STUDIES ON THE ECTOPARA.SITIC TEEMATODES OP JAPAN*. 165 



its wall presents in some species circular thickenings just as in some dis- 

 tomes ; and in many genera it is totally absent. Considering these cor- 

 respondences of the two canals I believe them to be homologous 

 structures — the Laurer's canal and the genito-intestinal 

 canal. As already mentioned in the historical portion, some writers 

 maintain that the Laurer's canal is homoloo^ous with the vao^lna of 

 the Monogenea ; but several considerations speak against this view. 

 Thus, the vagina of the monogenetic Trematodes opens in the mnjority 

 of species into the yolk-duct, and where it opens directly into the 

 oviduct it does so side by side with the yolk -ducts; while the Laurer's 

 canal mostly takes its origin dii-ectly from the oviduct. In Distomum 

 lupaticum, indeed, the Laurer's canal was supposed to open into the 

 yolk-duct, but Leuckart'^ and Poirier^^ have distinctly proved that 

 it opens not into the yolk-duct but into the oviduct, side by side with 

 the unpaired j'olk-duct. So far as I know, there only remains in this 

 respect the case oi Dist. cijliniraceum, in which, according to Monticelli,'' 

 the Laurer's canal opens into the yolk-reservoir. Now the difference 

 in this respect between the two canals under consideration will be 

 found by any one who will take the trouble to examine the actual state 

 of things in each particular case to be very much more considerable 

 than can be expressed by a single general statement (cf. e.g. the 

 various figures) ; and the single case above mentioned (which it is, 

 however, very desirable to examine more closely) can not be regarded 

 as a serious objection against my view. Then, the Laurer's canal 

 may, according to Monticelli*V ^^ regarded as " una continuazione 

 e dipendenza dell'ovidotto," since its wall has the same structure as 

 that of the latter. This, however, can not be maintained with any 



1). Leuokart— Die menschl. Parasiten. II. Aufl. pp. 53, 321, 238. 



2). Poirier— i. c. PI. XXX., fig. 4. 



3). Monticelli — Primo contributo etc. p. 106. 



4). I. .c p. 106. 



