BY WILLIAM A. HASWELL. 665 



the appearance of the nerve fibres of Trematodes and Cestodes run 

 forwards into a central mass of tissue having numerous particles 

 of pigment embedded in it. Though this, from its relation to the 

 nerve-fibres, is probably of the nature of a ganglion, it is scarcely 

 distinguishable from the surrounding parenchyma, and does not 

 contain a single cell that could be set down as a ganglion-cell. I 

 did not succeed in tracing any nerve cords in the hinder part of 

 the body. 



The only internal organs that are well developed are the system 

 of canals. A main trunk of considerable size runs along each 

 side. This frequently bifurcates, so that two main canals may run 

 parallel with one another through several segments — sometimes 

 again joining to form one, or one of them breaking up into 

 branches — the other continuing on as the main canal. The 

 branches given oflT are numerous and these again divide and sub- 

 divide ; the giving off of the branches has no regular relationship 

 to the segments. The main trunks do not extend quite to the 

 head end ; their posterior terminations, in the absence of complete 

 specimens, were not made out. 



On comparing these observations with what I can find published 

 regarding Ligula I observe many points of agreement. The 

 general shape of the body — elongate and ribbon-like with some- 

 what irregular segmentation — is the same in both cases. The 

 form of the head end is somewhat different apparently, and the 

 dorsal and ventral sucking grooves present in Ligula are absent in 

 the parasite of Hyla. 



The account of the minute structure of Ligula given by 

 Donnadieu* which is the only one, so far as I can ascertain, 

 published of recent years, leaves a great deal to be desired, and 

 has evidently not been drawn up from good preparations. The 

 cuticle (epiderme), he describes as in several layers (three are 

 represented in the figures) which increase in thickness from with- 

 out inwards, which are perfectly homogeneous. His representation 



* " Contributions k I'histoire de la Ligule ;" 'Journal de I'anatomie et de 

 la physiologie,' tome 13, 1877. The same remark applies to Duchamp's 

 " Recherches sur les Ligules" (Paris, 1876). 



