8 Dr. W. NicoU on the 



the ventral suckers depend largely on the method of killing. 

 Fresh water, for instance, causes the body to be much elon- 

 gated and the ventral sucker to be raised on a well-marked 

 pedicle. It also alters other relations, so that the neck 

 becomes much shorter and the breadth of the body is 

 decreased, while the thickness is greatly increased. In such 

 a condition the parasite agrees much more closely with 

 Odhner's description o£ Podocoti/le reflea'a than with his 

 description of P. a/07??on. Froni this it apj)ears that undue 

 importance must not be attaciicd to the elongated cylindrical 

 shape, with projecting ventral sucker, as in P. refiexa, unless 

 when dealing with specimens collected and preserved in a 

 unitorm manner. Under these conditions it may be safe to 

 differentiate, as Odhner has done, species such as P. reflexa 

 and P. ohsoiii, but at the same time it is probable that 

 Odhner's definitions are too comprehensive. Certain features 

 which he mentions are of undoubted specific value, and of 

 these I should put most reliance on the breadth of the body, 

 the length of the neck, and the length of the cirrus-pouch. 

 In none of my specimens, it may be noted, is the breadth less 

 than ^ or tiie neck less than ^ of the body-length. 



Admitting the specific identity of Podocotyle reflexa, it is 

 quite evident that my specimens from Gastnea spinachia are 

 not identical with Odhner's specimens from the same host, 

 for they are flattened ; the neck is much longer and the 

 breadth is greater than in that species. In addition the 

 testes do not occupy more than half the breadth of the body, 

 the cirrus-pouch extends only a short distance behind the 

 ventral sucker, the ovary is on the right side, and the yolk- 

 glands are in no case discontinuous at the level of the testes. 

 In fact the specimens are absolutely typical examples of 

 Podocotyle atomon apart from the large size of the ova. 



An immature example of the same ]>arasite was obtained 

 from the intestine of Onos tricirratus, this making the 

 twelfth British host of the species, all of these being rock- 

 pool fish with the exception of the plaice, as recorded by 

 Miss Lebour, and the flounder, as recorded by Johnstone. 

 Three additional hosts which I have to record from the West 

 Coast bring the total up to fifteen. 



[Lelouria) alacris, Lss. (PI. I. fig. 1.) 



From CalUonymus lyra a single specimen of a species 

 which can only with very great doubt be identified with 

 Jjistomum alacre, Lss. *, was obtained. It was 1*4 mm. 



• Centralbl. f. Bakt. xxix. p. 401. 



