DJSTOMA HEPATICUM. 257 



pressed in the spaces of the parenchyma left free by these con- 

 volutions. As soon as they have arrived at the level of the 

 ventral sucker, behind which they lie, and by which they are 

 concealed when the animal is examined from the ventral surface, 

 they converge still more, until at last they unite a little way 

 from the base of the sac of the penis, or vesica seminalis exterior, 

 forming a short, thick stem, opening into the last-mentioned 

 organ, and filling it with spermatozoids, which may be easily 

 effected merely by the help of the muscular contraction of the 

 abdomen. I have repeatedly been able to trace the course 

 of the two seminal filaments, from the point where they origi- 

 nate from the testicles to the vesica seminalis exterior. One 

 of these filaments is longer, and extends into the hinder half 

 of the Distomum ; the other usually originates a little way 

 behind the point of union of the yelk-sacs of the two sides, that 

 is to say, at the point of transition of the anterior third of the 

 whole Distomum into the middle third. From this doubling of 

 the filaments, follows the above-mentioned doubling of the testi- 

 cles, as we suppose that a testicle has only one efferent duct. 

 Taking into consideration the points to which these funiculi 

 spermatid may be traced, we spoke above of a posterior testicle 

 i. e., the one with the longer funic, spermat.), and an anterior 

 one (i. e., that with the shorter funic, spermat.) The point of 

 origin of each of these two filaments sometimes forms a sagittate 

 point, namely, when the last two or three lateral convolutions of 

 the penis, which are situated posteriorly or lateral, unite at a 

 very acute angle. 



The question still remains, whether, besides the above-men- 

 tioned outlets of the testicle, there may not be another communica- 

 tion with the egg-preparing organs, so that, as in other Trematoda, 

 self-impregnation might be possible without self-copulation, and 

 without an immersio penis. In Mehlis's figure viii we see the 

 foremost branch of the left side of the testicle opening into a 

 vesicular organ, which lies between the two funiculi spermatid, 

 and behind the point of union of the two yelk-sacs. I have also 

 seen this repeatedly, and it was not going too far to regard this 

 vesicular structure as a vesica seminalis interior, destined for self- 

 impregnation without copulation. But, as already observed, I 

 can only regard this vesicle as the germ-stock ; but I must con- 

 sider the anterior branch of the testicle just mentioned as the 

 substitute of the ves. sem. interna. If others succeed in detecting 



it 



