ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 197 



between the stomach and rectum ; they form quite a ridge on one side 

 by their close aggregation at this point ; they are surrounded by a 

 dense plexus of capillaries, and add considerably to the thickness of 

 the walls of the intestine ; most of the secretory tubules of the testis 

 converge towards the base of the stomach, where they unite in the 

 vas deferens which then crosses the body-cavity, accompanied by the 

 gastro-ovarian vessels, and unites with the oviduct at the anterior end 

 of the ovary. The ovary is a large oval body lying in the body-cavity 

 between the heart and the intestine, with a pointed anterior extremity 

 whence the oviduct, which is wide and has thin transparent walls, pro- 

 ceeds ; the gland is covered externally by the endothelium of the body- 

 cavity and is divided internally into large partitions by irregular 

 trabeculae of connective tissue ; the spaces contain ova in all stages 

 of development. The joint oviduct, vas deferens, and upper branchial 

 vessel meet the intestine near the end of its curvature and accompany 

 it to its termination, being attached along the line occupied by the 

 spermatic ridge on the interior. This ridge ceases to contain spermatic 

 glandules at the rectum. The joint cord executes a twist half round 

 the intestine ; being above it at the end of the curvature and below it 

 at the anus. The walls of the oviduct and vas deferens consist of a 

 thin lamina of connective tissue, covered externally by a pavement epi- 

 thelium consisting of one layer of small cells ; the internal epithelium 

 is ciliated in the oviduct, in some parts of the male duct it has the 

 character of an endothelium, the cells being broad and flat. The two 

 generative ducts open together in the cloacal cavity in a small beak- 

 like prominence which is terminated by a red organ. The orifice of 

 the oviduct is surrounded by muscle-fibres, that of the vas deferens by 

 about 10 to 15 small diverticula, inclosed in a sheath of connective 

 tissue ; the cavities of these diverticula are lined by large flat epithe- 

 lium-cells, behind which come two or three layers of orange-coloured 

 strongly granular cells, resting on the connective tissue, which is 

 perforated by numerous blood-capillaries. The orange cells contain 

 uric acid, oxalates (probably oxalate of lime) and phosphates, and. 

 their function must be renal. The spermatozoa arise from slightly 

 granular cells in which no nucleus was found and which are the outer 

 members of certain aggregations of cells into masses called polyplasts ; 

 in the outer cells of which appear hyaline spaces which are detached 

 as distinct non-nucleated cells, and accumulate outside their parent 

 cells ; they are the deuto-spermohlasts, and each produces a spermato- 

 zoon, whose head is attached to the parent cell until it is liberated. 



The circulatory system of this and other Ascidians is distin- 

 guished by the abundance of anastomotic branches of almost the same 

 calibre as the vessels which they connect. The circulatory currents 

 are thus indefinite in direction, and the distinction between venous 

 and arterial blood is not long maintained. Three main currents may, 

 however, be distinguished, viz. cardio-splanchnic, splanchno-branchial, 

 and branchio-cardiac ; the mantle receives small vessels from all the 

 organs which are in contact with it. The heart is bent on itself, and 

 gives off two vessels of equal length; it, togetLer with these, is con- 

 tained in a roomy Y-shaped pericardium. The mantle contains a 



