24 
CHARLES BADHAM. 
of dorso-ventral muscle fibres, which produce two or more 
lobes in a distended pouch. A sphincter of annular muscle 
fibres surrounds the tube just before and immediately behind 
the first pair of pouches, and dorso-ventral muscle fibres are 
also present about the neck of the following pouches and may 
act as sphincters. A similar arrangement has been described 
by Sukatschoff in Branchellion, but Johansson (1896) 
states that all the pouches of this part of the gut of Callob- 
della nod u lifer a have sphincters of annular muscle fibres. 
The anterior thin-walled part of the middle gut is followed 
ventrally by the blind gut (Text-fig. 6, B. g.), which in 
Austrobdeila consists of a pair of elongated pouches which 
open into the last pair of caeca of the thin-walled part of the 
middle gut. They extend back to the anal region and are 
fused with one another in five places. In fact the fusion is so 
complete that the parts which are not fused form merely four 
small apertures. When this blind gut region is filled with 
fish corpuscles there is seen on either side a series of caeca 
extending laterally, which decrease in size from before back- 
wards. The extent of the development of this blind gut has 
an important bearing on an interesting hypothesis put forth 
by Johansson (1898). All the thin-walled parts of the middle 
gut are lined by a single layer of flat 'epithelial cells, which 
become considerably stretched when a pouch is distended, but 
are well developed in the median parts. Weak muscle fibres 
are occasionally present, and the pouches are generally filled 
with undigested fish blood-corpuscles. 
A comparison of the blind gut region of Austrobdeila 
translucens with Johansson’s (1898) figures shows that here 
the development of the blind gut is intermediate to that found 
in Callobdella nodulifera and C. lophii. In this paper 
Johansson compares the structure of this blind gut region in 
the different Ichthyobdellids and divides them into three 
types. The first, and in his opinion the most primitive, type 
is represented exclusively by the genus Ab ranch us, which 
has two completely, or almost completely, separated blind 
pouches. The second type, represented exclusively by the 
