THE TREMATODA 



61 



The simple and archaic character of the intestine appears to be 

 related to the exceptional dorso-ventral thickness of the body, for 



J 



FIG. VIII. The Structure of Aspidocotylea, founded on that of Aspidogastcr. 



On the left, plan of the generative organs, seen from above. The alimentary canal is 

 indicated by dotted lines, in order to illustrate the dorsal position of the uterus throughout 

 the greater part of its extent, and its passage round the sides, to gain the ovary on the one hand 

 and the genital pore on the other, a, mouth ; 1>, pharynx ; c, the simple sac-like intestine ; (7, 

 genital pore (really ventral in position) leading into the genital atrium ; e, the copulatory 

 region of the uterus surrounded by glandular tissue ; /, the uterus, long, undulating, as in a 

 Distome, and dorsal in position ; g, vitellaria, with a longitudinal duct on each side connected 

 by a transverse vitelline duct to open by a short common duct into the germ duct{A) ; f , ootype, 

 surrounded by the shell gland ; j, Laurer's canal (=recept. yitelli of Voeltzkow), arising from 

 the germ duct and passing backwards to terminate in a pyriform dilatation 0'') j"t below the 

 skin of the dorsal surface, immediately behind the end of the intestine ; A', gennarium ; I, 

 testis, here a single "compact" organ; m, sperm duct; n, seminal vesicle; p, penis, sur- 

 rounded by prostate gland ; s is the outline of the sucker which just projects beyond the 

 margin of the body ; t, outline of body. 



On the right, plan of the excretory system, a, excretory pore (there are two, according to 

 Stafford) ; b, the great collecting vessels or ducts dilated posteriorly to form a bladder ; c, 

 excretory tubule arising from its anterior end and passing into the neck ; d, the recurrent 

 limb; from the point marked by the index line there are, in the whole course of the system, 

 bunches of cilia (Hames) set close together along the mesial wall of the tubes. This main tube 

 gives off branches (e) which, according to Stafford, always came off in 3's, and the subsequent 

 branching is also in 3's ; after six such trifurcations the finest capillaries terminate in flame 

 cells. This figure was drawn before Stafford's paper appeared, and is schematised from 

 Voeltzkow's side view ; he, like Huxley, described the right and left canals as asymmetrical, as 

 here represented ; Stafford believes them to be symmetrical ; kf, the branch from left canal to the 

 gennarium; I', the branch to the testis; ', the branch to the sucker; according to Stafford, 

 similar branches issue from the right canal as well. 



the reproductive organs can attain their full size and development 

 without compressing the gut and interfering with its primitive 

 sac-like form. The wall of the intestine, as well as that of the 



