644 Proceedings of Royal Society of Edinburgh. [sess. 
succeeding one. All the specimens that I had occasion to study 
were strongly contracted. The measurements given above have 
therefore no absolute value, for they vary according to the degree 
of the contraction of the animal. The scolex is unarmed, without 
rostellum and hooks ; it has the typical shape of the head of the 
Prosthecocotyle species. The head differs from the drawing pub- 
lished by 0. Linstow, as may be seen by comparing fig. 17 of 
Linstow with my fig. 1 drawn with Abbe’s drawing apparatus. 
The scolex is 1 mm. wide and about 2 mm. long. Its shape 
is quadrangular. This singular form is produced by the pro- 
trusions of the suckers characteristic of all Prosthecocotylce. These 
are the suckers that exhibit anteriorly and externally ear-shaped 
protrusions, which have the same structure as the suckers. The 
suckers with their small openings lie on the dorsal and ventral side 
of the scolex; they are oval, with a long diameter of 0'34 mm. 
and a transverse diameter of 0’23 mm. They touch one another 
in the median line of the head, and are very powerful and deep. 
Unhappily, I cannot give information on the histological structure 
of this interesting scolex, because I could not make sections of it. 
Neither can I state whether the posterior part behind the head is 
normal. 
The segments, which are very short and thick, and separated by 
a deep incision, are covered by the cuticula and the subcuticular 
layer of cells. The cellular structure of the parenchyma is distinct 
everywhere; it is not crossed over by muscular fibres. We find it 
so in the lateral extremities of the internal parenchyma and in 
the cirrus-pouch. The calcareous corpuscles are found specially 
in the external parenchyma, but also between the muscles and in 
the intermediate layer of parenchyma situated between two seg- 
ments. In the ripe segments they are particularly numerous in 
the lateral parts of the internal parenchyma, where one can study 
their development out of the cells of the parenchyma. 
We find directly under the cuticula a simple layer of circular 
and longitudinal fibres. In the parenchyma we discover two 
layers of longitudinal muscles. The external stratum is formed by 
small bundles of spindular fibres ( ca . 10 fibres). This thickly 
laid stratum of muscles envelops completely the central part of 
the segment, and is only interrupted at the point where the 
