DEVELOPMENT OF BALANOGLOSSUS KOWALEVSRKII. 527 
(8, g.s.}. At their origin they are simple conical funnels, but 
they soon acquire a crescentic lumen owing to a thickened 
inward folding of their outer wall. This is not conspicuous in 
B. Kowalevskii (ep. figs. 88 and 104). Their histology is 
sufficiently indicated in the figures. 
As previously mentioned, the blood-vessels consist of 
(1) a dorsal vessel leading from the heart to the tail; (2) a 
ventral vessel running from the back of the collar to the tail; 
(3) in B. minutus a pair of large lateral vessels (v. fig. 93) 
in the digestive region. These are connected by piexuses in 
the skin and under the epithelium of the gut. In the operculum 
this capillary system of the skin forms a more or less definite 
circular vessel. In parts of their course these vessels are always 
more or less filled with a fibrous-looking substance, apparently 
cellular, which lines the walls (fig. 71). The generative 
organs lie in blood-sinuses derived from the subcutaneous 
plexus. 
I stated (“‘ Later Stages,” &c.) that the branchial blood-supply 
resembled that of Amphioxus. From further observation I 
have come to the conclusion that this is a mistake, and that 
the vessels supplying the gills are all derived from the dorsal 
vessel, as Spengel has stated, being, in fact, merely the skin 
capillaries of the dorso-lateral regions. The main vascular 
trunks are all formed from the mesoblast of the first cavity 
and of the third pair of cavities. The capillaries under the 
’ skin and round the gut are formed in sit& in the mesoblastic 
walls in which they occur. 
The Generative Organs, 
The Ovaries.—The animals are all diccious. The origin 
of the ovaries is not certain, but there is very strong evidence 
that they are epiblastic. At all events, from almost their 
earliest appearance, they are connected with the skin in the 
dorso-lateral regions (v. fig. 110). It is almost impossible to 
believe that an attachment of this kind is secondary, and I 
have never seen an ovarian follicle entirely separate in the 
body cavity. 
