EPIZOA. 



149 



distinguished in their mature state by a body of a more or less 

 elongated or sub-cylindrical form, defended by a smooth, semi- 

 transparent, parchment-like integument, having a more or less distinct 

 head, and generally a pair of long cylindrical ovisacs, dependent from 

 the opposite extremity of the body. 



In this low organised class of Articulate animals, as in the classes 

 which commence all other great primary groups, there is an extensive 

 gradation of forms by which we pass from species 

 slightly elevated above the cavitary Entozoa to the 

 true Crustaceans. 



The lowest or most simple Epizoa adhere by a 

 suctorious mouth {^fig. 79. «), and traces of extre- 

 mities exist only in the form of a few minute pairs 

 of obtuse inarticulate processes {h b). In the 

 j\ highest organised species, the adhesion is effected 



by jointed mandibles with terminal hooks or for- 

 ceps. The head, in most of the species, is found, 

 when closely examined, to present a pair of jointed 

 antennae {Jig. 81. e), which, in the experienced na- 

 turalist, cognisant of the value of such characters, 

 might excite the suspicion that relations to higher 

 Articulata than the Anellides were hidden under 

 the bloated form which indolent and gluttonous 

 habits had superinduced upon the pendent parasite. 

 Observation of it during its early and independent 

 state has proved this to be actually the case to an 

 extent which could scarcely have been anticipated. 

 The Epizoa are of distinct sexes : the male {Jig. 

 82.) appears always to retain his freedom, and is, 

 perhaps on that account, singularly smaller than the 

 female, generally not more than a fifth part of her 

 size ; consequently, for a long time, the males es- 

 caped recognition. They adhere to the vulva with 

 one antenna usually inserted. The individuals 

 of the productive sex, distinguished throughout a 

 great part of the year by their pendent ovisacs, are 

 the examples usually seen of this curious class ; 

 and in these I shall proceed to describe the ana- 

 tomical characters of the Epizoa. 



The body, independently of the ovisacs, is gene- 

 rally divided into two segments : the anterior and 

 smaller division sometimes supports a distinct head, but more com- 

 monly corresponds with the cephalothorax of the Crustacea; the larger 



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