416 Mr. H. A. Baylis on Octopelalum, a 



width occurs rather behind the middle of the strobila. The 

 last four or five segments are from two to three times as long 

 as broad, the last being the longest and narrowest. In one 

 specimen the last segment measured 1 mm. broad and 

 3'5 mm. long. 



Tiie hinder border of each segment overlaps the following 

 segment considerably. The genital apertures are irregularly 

 alternate. They are situated at about the middle of the 

 lateral border in young and sexually mature segments, but 

 the aperture becomes shifted relatively backwards to about 

 the posterior third of a gravid segment, owing to its elongation 

 in front to make room for the paruterine organ, which will 

 be described below. 



Internal Anatomy. 



Musculature. — Between the subcuticular layer of the body- 

 wall and the central or medullary portion of the body there 

 is a very considerable thickness of longitudinal muscle- 

 bundles, of which the outer rows are the smallest, and the 

 innermost rows the thickest and strongest. Internal to these 

 there is a layer of fine transverse fibres, which surround the 

 medullary parencliyme, in which the genital organs are em- 

 bedded, and extend round, and slightly beyond, the large 

 excretory canal and nerve on either side of the body. 



Nervous St/ stem. — A pair of large lateral nerve- cords is 

 present as usual ; they are situated close against the excretory 

 canals, lateral of them, and slightly to the (supposed) dorsal 

 side. 



Kxcretory System. — Only one pair of longitudinal excretory 

 canals can be lound, and these are of a very remarkable size, 

 J)aving a diameter nearly equal to the deplh of the medullary 

 region. They are connected at the hinder border of each 

 proglottis by a transverse vessel. As this connection exists 

 between the ventral of the two pairs of vessels in the majority 

 of Cestodes, and as, in the other cases wiiere only one pair 

 occurs, it is held to be the dorsal pair that has become reduced 

 to the point of disappearance, it seems legitimate to assume 

 that in the present case the single pair of large canals repre- 

 sents the ventral pair (or possibly the dorsal and ventral 

 pairs, which have coalesced). This enables us to fix upon 

 an orientation of the animal which will serve for purposes of 

 description. Assuming that the genital ducts pass to the 

 dorsal side of the ventral excretory canals, as is usually the 

 case, we may call that side dorsal, and in that sense the word 

 will be used throughout the description. 



