STUDIES 0>* THE ECTOPAEASITIC TREMATODES OF JAP AX. HJ 



in all the other species it opens into the genital atrium at various dis- 

 tances from its external opening (PL XXI, Hg. 8; PL XXII, fig. 2; 

 PL XXV, figs. 3, 8, and 9). 



As already mentioned above, there are in this "-enus t\\(j sets of 

 muscular fibres in the loose connective tissue around the uterus, which 

 are exactly similar to, and one of which is the direct continuation of, 

 those around the ootyp. The dorso-ventral fibres are present only a- 

 round the lower part of the uterus; but the horizontal fibres are con- 

 tinued to the margin of the body, where they become continuous with 

 the diagonal fibres of the body (PL XXII, fig. 4). 



A''itellaeium — This is a very extensive organ situated mostly 

 in the lateral portions of the body and extending through the 

 greater part, or in some species throughout the whole length, 

 of the body (Tristomiim, Epihdella). In accordance with its position 

 in the bodj?^, it consists of two parts, a right and a left half, 

 which remain in many species entirely distinct throughout their 

 whole extent ; but in other species they pass into each other 

 at both ends. Again, in most species, the vitellarium seems 

 to be closely connected with the intestine in its arrangement, be- 

 ginning and ending with the main intestinal trunks. In Microcoiyle 

 this relation is especially conspicuous. As already mentioned, the 

 two trunks of the intestine are in some species of this genus of unequal 



lengths : and then the halves of the vitellarium also show a cor- 

 es ' 



responding asymmetry, as in M. elegans (PL I, fig. 4) and M. sciaence 

 (PL II, fig. 6). There are, however, also species in which the vitel- 

 larium and the intestinal trunks do not show any correspondence of 

 lengths, as M. caiidata and M. sehastis (PL I, figs. 1 & 2). Again, in 

 many species in which lateral bi'anches of the intestinal trunks are 

 given off towards the median line, these ai"e accompanied by the vitel- 

 larium, which then surrounds them on all sides. In Axine, Microcotyle, 



