16 s. GOTO. 



1)0 flemonstrated in cross-sections ; so that the laver of lonfritudinal 

 fibres seem in such sections to be separated from the investing mem- 

 brane only by a layer of mesenchyma (PI. Ill, fig. 4). 



The dorso-ventral muscular fibres are developed in very different 

 degrees in different species, but they are, so far as I have observed, 

 never wanting. They are but weakly developed in Axine and in most 

 species of ^ficwcotijle ; moderately in Diclidophom, HexacoUjJc, Onclwco- 

 ijjJe and Monocoti/Je ; and very strongly in Tristoimim. It is, as is 

 w^ell known, the characteristic of tlie dorso-ventral fibres that they 

 ramify into a number of fine branches towards their ends, and are 

 inserted onto the investins; membrane of the body. Thev nlso traverse 

 some internal organs, such as the testes and the vitellarium. 



In MotiocofjiJr there are in the hindmost portion of the body 

 an assemblage of striped muscular fibres (PI. XVII, hg. 5) ; but as 

 these are present mainly in the posterior sucker, they will be described 

 in that connection. 



4. The Organs of AttacltmrnL 



Under this head I include the suckers, both true and rudimen- 

 tary, the glands, which subserve, according to my opinion, the same 

 purpose, and the hooks. These, but es])ecially the glands, are more 

 numerous and of more varied structure than has hitherto been thought. 



SucKEKS — The suckers may be classed, for the sake of description, 

 into the anterior and the posterior suckers, of which the latter present 

 more variety of structure than the former. The differences in both of 

 them are characteristic of the genera, and so will be treated separately 

 under each genus, except where another treatment is more desiraljle. 



Microcotyle and Ax'uie — In these two genera the anterior 

 and posterior suckers are of the same structure. They will therefore 

 be treated of toirether and minor differences occasionally noted. 



