Entozoa of British Marine Fishes. 21 



oven a small part of the viscera extend into the appendicular 

 part, the true funclion of which reniain.s unelucidated. The 

 older term ** appenclix " ia much more appiicaljle; but if 

 exc«j)tion is tuki-n to that it is not ditRcult to coin a word, 

 e. g. ecsoma (the part out of the body), much more a])propriate 

 than abdomen. 'I'he term introvert seems quite as suitable as 

 any, even althouj^h it is used to describe different special 

 or^'ans in various groups of animals. 



Kccent work may be considered to have faiily well 

 established the specific characters of Ileniiurus comuiu'iis, hnt 

 there are still one or two |)oints otj which absidute uniformity 

 does not exist. The length of the soma is 1-3 mm. Tho 

 average breadth is about ^ of the length of the soma, greatest 

 just before the junction with the ecsoraa. The latter is at 

 most 5|, frequently Ks;*, of the length of the soma. Tiie neck 

 (distiince of the ventral sucker from the anterior end) ia 

 about .^ of the length of the soma. These measurements 

 have been agreed on by every observer, but in connection 

 with the sizes of the suckers my results are at variance with 

 those of others. Both Odhner and Miss Lebour * give the 

 ratio as approximately 1 : 2, but I have never yet found a 

 specimen in which the ventral sucker was twice as great as 

 the oral sucker. I find the ratio always greater than 1 : 2 

 and often as much as 2 : 3. There is tlierefore no difference 

 in this respect between IJemiurus coinniunis and //. liihei. 

 Wherein the difference between the two species really con- 

 sists is that in //. liihei the suckers are proportionately much 

 smaller than in //. comtniinis. In the latter the diameter of 

 the ventral sucker is about j of the length of the soma, but 

 it may be as small as }j or as large as -g, depending to a great 

 extent on the state of contraction. In //. liihei the ventral 

 sucker rarely exceeds |*j of the length of the soma. In 

 II. communis the oesophagus is nearly equal to the pharynx 

 in length. The genital sinus does not extend backwards as 

 far as the ventral sucker ; the [)ars prostatica is of moderate 

 length. The vesicula seminalis is bipartite, thin-walled, and 

 situated just behind the ventral sucker. The testes are 

 placed immediately behind the vesicula seminalis, always 

 n ore or less obliquely behind each other. The ovary ia 

 sejtarated from the testes by \ of the length of the soma. 



Jlemiurns liihei, Odhner. 



Hitherto this species has only been found in the herring 



• In Miss Lebour 8 fig^ure of Ilemiurus cummuni$ the sucker-ratio ia, 

 by oicasurement, exactly 2 : 3. 



