ASCIDIA. 65 
coarser tubules of the ovary and the adjacent parts of the 
intestinal wall. These spermatic tubules terminate in 
ovate swellings, usually grouped in bunches (Pl. IV., 
fig. 15). Near the commencement of the rectum the larger 
tubules unite to form the vas deferens, a tube of consider- 
able size which runs forward alongside the rectum, and, 
like the oviduct, terminates’ by opening into the peri- 
branchial cavity close to the anus. The lumen of the 
tubules of the testis, like the cavity of the ovary, is a meso- 
blastic space in the embryo, and the spermatozoa are 
formed from the cells lining the wall, and are set free into 
the cavity. 
The mature ovum is of small size (about 0°12 mm. in 
diam.), colourless, and with little or no food yolk in the case 
of Ascidia. It is only some of the germinal cells in the 
ovary that are destined to become ova. Of the rest, some 
form a protecting layer, the follicle, around the young ova. 
Certain of these primary follicle cells migrate inwards and 
give rise, by proliferation, to a layer of cells in the superficial 
part of the ovum (PI. V., fig. 1, ¢.c.). These are the 
so-called “‘ testa-cells”’ or kalymmocytes. These later on 
produce a thin gelatinous layer over the surface of the 
ovum and between it and the follicle, which looks like 
the beginning of the test—hence the name given to the 
cells, which, although so different in origin from the 
mesodermal test cells of the adult, probably to some 
extent give rise to “ bladder cells” in the test. The rest 
of the follicular “‘ testa-cells’’ eventually disappear. 
The follicle cells proper produce two layers, the outer of 
which remains in the wall of the ovary when the ovum is 
set free; while the inner layer adheres to the surface (PI. 
V., fig. 1, foll.), and its cells become large and much vacuo- 
lated, some of them growing out to form long papilla, 
which help to sustain the floating egg in the sea-water. 
