Anatomical structure of Aspidogaster conchicola. 519 



distended seminal vesicle the walls are thin and the nuclei widely 

 separated. In the living worm the vesicula seminalis is easily recog- 

 nized from its grayish color, its considerable size and its serpentiform 

 windings. In it, besides the filiform spermatozoa which are packed 

 and interwoven into a great mass, with here and there more loose 

 transparent places in which the sperm may be seen in rapid motions, 

 there are large brightly glistening, strongly refracting globules. In 

 sections stained in haematoxyliu the sperm cells are purplish, their 

 heads recognizable as little dots scattered through the less deeply 

 colored mass of curved tails. Refractive globules are not to be seen 

 but corresponding with their positions are irregular spaces no doubt 

 left as the former became dissolved in the preparing fluids. My 

 impression is that they are drops of secretion extruded with the sperm 

 to preserve and float them out. Regarding the origin of such a sec- 

 retion it may be that the mass of cells round the testis can to iome 

 extent function as unicellular glands. I have seen some of them with 

 a tapering towards the wall of the testis but their closeness to this 

 organ and their density make it difficult to get a clear view. 



At its anterior end the vesicula seminalis passes into the penis 

 sack. The position of this organ is generally in the long axis of 

 the animal as it is heavier than the vagina but sometimes it lies a 

 little to the right and it may also be curved out of the direct course. 

 It is a strong muscular sack of 0,15 mm in diameter and 0,5 mm in 

 length but narrowing a little as it passes forwards until its inner left 

 wall meets with the inner right wall of the vagina, and its outer wall 

 with that of the vagina bound the opening of the genital sinus. The 

 cirrus sack is composed of a strong inner circular muscle layer 

 (Fig. 18 PSC) and a still thicker outer longitudinal muscle layer. In 

 cross sections the outer muscles appear in bundles. Round the posterior 

 half are the deeply staining unicellular prostate glands (Fig. 9, 

 12 Pa) the ducts of which pierce the penis sack between its muscle 

 bundles. 



Through the axis of the penis sack stretches the ductus eja- 

 culatorius (Fig. 16, 18 J) which however does not assume the 

 form of a simple duct except in its middle portion the walls of its 

 anterior end being thickened and folded to produce the extrusible 

 penis (Fig. 9, 16, 2 CO) proper or organ of coition while its posterior 

 division through a complex system of expansions, reflections and foldings 

 produces the large structure filling the posterior end of the penis sack 

 which has been fitly designated the bulbus. To understand the 



