418 Mr. H. A. Baylis on Octopetalum, a 



to contain a single layer of eggs) is left below, connecting 

 the two wider parts. 



In the older proglottides, as the testes and other organs 

 disappear, the uterus, which now appears to be a single large 

 sac, takes up a larger proportion of tiie space, so that even- 

 tually it occupies the whole of the posterior half, being 

 bounded laterally and posteriorly by the excretory vessels. 



Meanwhile the anterior part of the segment has become 

 elongated, and a remarkable cliange has taken place in it. 

 A *' paruterine organ " is developed, extending from the 

 anterior border of tlie uterus nearly to the anterior limit of 

 the segment. It is of a fibrous structure, and seems to be in 

 direct communication with the ulerus beliind ; but, curiously 

 enough, no eggs were observed to have passed into it in any 

 of the specimens, although this usually liappens in forms in 

 which such an organ is present. The uterus, in the most 

 advanced segments, was quite full of large ova containing 

 onchospheres, but the paruterine organ was invariably empty. 

 Tills may, perhaps, be accounted for by supposing that the 

 still older segments, in which the migration of the eggs had 

 occurred, had dropped off. 



The eggs contained in the uterus in the oldest segments 

 are invested with three transparent membranous envelopes. 

 The outer envelope is thin, and measures from 87*5 fj, to 

 100 fjb in diameter. The middle envelope is thicker (2"5 yu.) 

 and has a diameter of 50 /jl. The innermost is a very thin 

 membrane closely surrounding the embryo, wiiich is an 

 onchosphere, bearing hooks from 17"5 /j, to 20 /j, long. 



Note on the Systematic Position of the Genus. 

 In its external appearance, and particularly in the possession 

 of " auricular appendages " of the suckers, this form closely 

 resembles Tetrahothrius. The following features, however, 

 show considerable divergence: — 



Tetrabothrius. 



1. Geuital pores unilateral (all 

 ou riu-ht side). 



2. Yolk-giand ventral and in 

 front of ovary. 



3. Cirrus-sac separated from 

 genital atrium by narrow muscular 

 passage (" male cloacal canal," 

 Fuhrmann). 



4. Vagina ventral to cirrus- 

 sac, in same vertical plane. 



6. No paruterine organ. 

 [6. Two pairs of longitudinal 

 excretory canals.] 



Octopetalum. 



1. Genital pores irregularly alter- 

 nating. 



2. Yoik-glaud dorsal to ovary 

 and in posterior part of segment. 



'6. Cirrus-sac communicating 

 directly with genital atrium. No 

 muscular passage, 



4. Vagina posterior to cirrus-sac, 

 in same horizontal plane. 



5. A paruterine organ present. 

 [6. One pair of longitudinal 



excretory canals.] 



