DEVELOPMENT OF BALANOGLOSSUS KOWALEVSKII. 521 
and bear a few long cilia. In the walls of the gut in this 
region are numerous blood-vessels. The lumen of the gut in 
this region varies greatly in size, probably with the digestive 
processes (cf. Salensky, loc. cit.), the liver being in 
B. Kowalevskii occasionally obliterated. 
In B. Kowalevskii there is no distinct sacculation to 
form the liver, but in B. minutus the dorso-lateral walls of 
the digestive region are pushed out to form the characteristic 
liver outgrowths. These structures are not regularly paired. 
Their walls are full of secondary foldings (v. fig. 93). The 
cells lining these folds are similar to those of the digestive 
tract, containing large granules and fluid-looking vacuoles. 
The skin covering these liver-saccules is very thin, and in 
B. salmoneus it may often be seen fused with the 
hy poblast, forming openings which place the cavity 
of the liver diverticula into actuai connection with 
the exterior. The histological appearances are such as to 
leave no doubt that an actual fusion occurs. When the 
extreme softness of the tissue is remembered, it seems likely 
that these perforations may, in the first instance, be due to 
wounds which have healed so as to form fistule. [In a single 
case of B. minutus a fistula of this kind was found forming 
a perforation from the intestine to the body cavity. In this 
animal the fusion between hypoblast and mesoblast was quite 
complete. | 
The liver of B. salmoneus is dark green in colour, and this 
colour is due to minute round granules or drops in the hypo- 
blast. In B. Robinii the tint is generally dark brown. 
The histology of the intestine, which is usually more or 
less diamond-shape, two of the angles being dorsal and ventral, 
is in no way remarkable. From the first the wall is formed 
of asingle layer of cells, ciliated, and smaller than those of 
the digestive region (v. fig. 83). The anus opens imme- 
diately above the tail until this structure disappears, and then 
it opens widely in a terminal position (v. figs. 83 and 6). 
