648 Proceedings of Poyal Society of Edinburgh. [skss. 
formation of the envelopes of the eggs ? As I have just said, 
the eggs remain for a long time without shells, and are very poor 
in vitellus; it is only in the last segments that one finds the 
embryo with its six hooks enveloped by three shells (diameter of 
the embryo and the first envelope 0036 mm. ; hooks, 0"014 mm. ; 
diameter of the second envelope 0-039 mm. ; diameter of the third 
envelope 0’054 mm.). In the segments which are quite ripe, the 
sexual glands have completely disappeared and the uterus fills up 
the internal parenchyma. 
Prosthecocotyle heterodita (Dies.). 
Syn. Tetrabothrium lieteroclitum (Dies.), Amphoteracotyle elegans 
(Dies.), Tetrabothrium auriculatum (Linstow). Digs. 4-7. 
A serious comparative study of the originals of T. auriculatum 
and of Diesing’s examples of T. heteroditum has shown me that 
the two species are identical. This interesting Taenia was found 
in the intestines of Thalassoeca glacialoides , Smith, and Daption 
capensis (Linn.). According to Linstow, the animal attains a 
length of 112 mm. ; the scolex is 0‘48 mm. in breadth and 0 - 34 
mm. in length. According to my measurement the breadth of the 
head is of 0*38 mm. The powerful suckers occupy almost the 
whole of the scolex, and each one exhibits anteriorly and ex- 
ternally an ear-shaped protrusion. “At a distance of 0‘6 mm. 
behind the scolex the segmentation begins. The first proglottides 
are 0012 mm. long and 0'41 mm. broad; those in the middle are 
0*29 mm. by D64 mm., while those furthest back measure 0*42 
mm. in length by 2*5 mm. in breadth.” This worm has not such 
a great thickness as P. torulosa, but is, on the contrary, very 
flat. Also the proglottides are a little longer than in that species, 
but the separation of the proglottides is equally distinct, and the 
separation between each segment reaches the longitudinal muscles. 
In the external parenchyma numerous calcareous corpuscles are 
found. The internal parenchyma is reduced by the development 
of the sexual glands. 
Besides the subcuticular musculature, which shows nothing very 
remarkable, we find, as in P . torulosa , a double zone of bundles 
of longitudinal muscles, the external ones of which are less strong. 
