EEPOET ON THE THNICATA. 
23 
Ascicliozooids in some species (see fig. 3, p. 16, v.ap.; and PL V. fig. 13), are really 
diverticula of the mantle, and are composed of a layer of ectoderm and, inside that, of con- 
nective tissue containing two blood sinuses running side by side, and therefore correspond 
to the blood-vessels of the test in Simple and some Compound Ascidians. The vascular 
appendages may in some cases {e.g., Colella concreta, and many of the Didemnidse) 
contain muscle fibres continuous with the musculature of the mantle. Blood sinuses or 
lacunae are present in all parts of the body, and form the greater part of the circulatory 
system. 
A mass of a glandular nature, and having usually a yellowish-green colour, which 
coats the first part of the intestine, is in aU probability of a renal nature, and corresponds 
to the renal vesicles found in many Simple Ascidians {e.g., Ascidia mammillata, Ascidia 
meridionalis, &c.). 
The Reproductive Organs. 
The Ascidiozooids are probably in all cases hermaphrodite, but in many forms the ova 
and the spermatozoa are produced at different times, and are therefore not found mature 
together. The usual arrangement ^ is for the ova to form first, and then after they have 
been laid or have passed into the incubatory pouch the spermatic vesicles commence 
to develop. This protogynous arrangement of course prevents self-fertilisation. 
The genital glands may be placed on the sides of the branchial sac, as in the 
Botryllidse, where there is usually an ovary and a group of spermatic vesicles upon each 
side of the body (see PI. II. figs. 10, 11). A more usual arrangement is for the genital 
glands to be placed in the intestinal loop, either alongside the intestine as in the Distomidse, 
Didemnidse, &c. (PI. V. fig. 13), or projecting beyond the intestine posteriorly to form 
a shorter or longer post-abdomen (fig. 3, p. 16) as in the Polyclinidse (PI. XXL fig. 5). 
The ovary is simply a group of more or less completely developed ova and germinal 
cells (PI. VII. fig. 7), and there is probably no true oviduct present.^ The spermatozoa 
may be formed in a single large testis (as in Didemnuni savignii, PI. XXXIV. fig. 2) or 
in a large number of small testes or spermatic vesicles (fig. 3, p. 16) which vary in shape 
and arrangement in the different groups (see descriptions of the genera and species in 
the Systematic Part of the Eeport). A distinct vas deferens is always present, aud it is 
usually a very cons23icuous tube which runs alongside the rectum in its entire length 
(PL XXV. fig. 6). In some cases {Leptoclinum speciosum) the vas deferens commences 
by coiling spirally around the large testis. In other forms the vas deferens is convoluted 
in its entire course. It opens into the peribranchial cavity close to the anus. 
1 Della Valle states that most are protanilrous. That is not my experience, as will he seen in the description of 
the species further on in the Report, see also Summary at end. 
2 The evidence in regard to the oviduct is very conflicting. Some observers describe it as being present in many 
forms, others say that it is never found in any Compound Ascidian. I have been unable to find it in any I have 
examined. 
