95 



■wliicli open into it on each side are ventral in position. The ovai-y is a flattened sac 

 with a circular outline situated immediately behind the yolk-reservoir. It is filled with 

 small spherical ova, each containing a large nucleus or germinal vesicle. In front of 

 the ovar)% dorsal to the right main yolk-duct, is a sac with the shape of a pyramid. 

 Into this sac or vestibule open a short oviduct from the ovary, a short duct from the 

 yolk-reservoir, and two minute short ducts from two spherical capsules containing 

 spermatozoa. Here the egg is fertilised. From the vestibule the oviduct is continued 

 for some distance as a narrow convoluted tube, which then suddenly expands into a 

 thick-walled sac shaped like a club, the thick end being internal, and the thin end 

 opening to the exterior on the edge of the body to the left of the anterior apex. This 

 thick-walled sac may be called the uterus. The fertilised ovum in the vestibule is 

 surrounded by a quantity of yolk, and the compound mass thus formed passes down the 

 oviduct to the uterus, where it is surrounded by a chitiuous hard shell produced from 

 the wall of the uterus The shell has the shape of a triangular pyramid, and its apex 

 is prolonged into a long thin filament, swelling at intervals into bead-like globules. 

 This filament is doubtless adhesive, and by it the egg when laid, Fig. C, is attached to 

 the skin of the sole, there to develop into a young Phyllonella. 



The primary male organs are a pair of globular testes situated a short distance 

 behind the ovary, one on each side of the middle line. These testes are simple sacs, 

 the walls of which are lined by cells which give rise to the spermatozoa. Some of 

 these cells become free in the cavity of the testis, and undergo subdivision, each of 

 them forming a spherical cluster of small cells, the spermatoblasts, each of which is 

 converted into a spermatozoon. From the anterior surface of each testis passes off a 

 tube or duct, the vas deferens ; the two ducts unite just behind the ovary, and the 

 single vas deferens passes round the left side of the ovary, and the left side of the j'^olk- 

 reservoir, dorsal to the left main yolk-duct. In the part of its course which lies in 

 contact with the yolk-reservoir the vas deferens is connected with a coiled sac closed 

 at its farther end. This is a reservoir for the ripe spermatozoa, and must be called the 

 vesicula seininalis. After a tortuous course the vas deferens opens into an intromittent 

 organ, the penis. The mechanism of this organ I have not been able completely 

 to elucidate. It consists principally of a club-shaped structure lying between the 

 uterus and the alimentary sac. Along its outer half this structure contains a canal, 

 which is at the side of it, not in the centre : into this canal the vas deferens opens, 

 and by it the spermatic fluid is convej^ed to the exterior. The inner half of the 

 structure contains granular matter, but, as far as I can make it out, is not a gland. 

 At the base of the penis is a pear-shaped structure with radiating bands in its interior, 

 which converge into a band apparently of muscle, which seems to run into and become 

 merged in the substance of the penis. I am inclined to think that these structures 

 have something to do with the protrusion and retraction of the penis, but I am unable 

 to understand how thev act. 



In the chief features of its structure P/u/llonella solece resembles a number of other 



