OCR Text |
Show 1904.] DISCOVERED TURBELLARIAN WORM. 409 Reproductive System (Plate XXV. figs. 6, 7). A. incola is hermaphrodite and is found sexually mature at Millport, N.B., in June and July. The penis is situated on the ventral surface at the junction of the posterior fourth with the rest of the body. It is conical and carries a knob-like armature at its distal end. At its proximal end its duct dilates to form a pyriform vesicula seminalis, the walls of which are formed by a thickening of the surrounding dermal parenchym and into which the testes open on either side by no distinct or epithelially lined channels. The testes consist of follicular masses extending forwards on either side in the parenchym of the lateral parts of the body, outside the ovaries, to beyond the mouth, and posteriorly also for a short distance into the tail. The sperm-follicles near the vesicula seminalis contain deeply staining chromatin figures. The ovaries extend on either side of the middle line from beneath the brain to within a short distance of the male apparatus. They early unite, but are soon separated by the digestive vacuole, joining again in the posterior middle fourth of the body (figs. 1, 2). The ova increase in size as they pass backwards and are enclosed in delicate parenchyma, each occupying latterly a separate " follicle." N o accessory female organs are present. There is no vagina through which the ova can be extruded, and it would appear from a careful examination of ripe specimens that the cuticle simply gives way before the ripe ovum owing to an ever-increasing growth-pressure- this rupture taking place at a short distance in front of the penis (fig. 7). In several examples the ova lying most posteriorly had acquired a relatively dense capsule, stainable with osmic acid, and these not infrequently showed mitotic figures. These facts, taken in relation with the armature of the penis, seem to point to copulation being effected by simple perforation of the cuticle. SYSTEMATIC POSITION, The turbellarian now described differs along with all the species of Haplodiscus from other Accela in that it possesses no female accessoria. From Haplodiscus also it differs in the following respects:- (1) Shape. (2) Parasitic habitat. (3) Mouth in anterior fourth. (4) Paired lateral testes. (5) N o defined vasa deferentia. (6) Penis with knob-like armature. (7) Frontal organ well developed and opening by many mouths. (8) Large digestive vacuole. These differences seem to be of sufficient importance to warrant the erection of a new genus, which I have called Avagina. As an |