50 



INTRODUCTION TO CLASSIFICATION. 



what these can correspond if not with some modification of the 

 water-vascular system.* 



Fig. 24. 



Fig. 24. The Echinorhynchus of the Flounder. A. Diagram exhibiting the relative 

 position of the organs, a. Proboscis, b. Its stem. c. Anterior enlargement, d. 

 Body. e. Posterior " funnel.'' /. Neck. g. Meniscus, h. Superior oblique tubu- 

 lar band?, k. Inferior muscles of the proboscis. /, m. Genitalia. o. Penis, or 

 vulva. B. Lower extremity of the stem of the proboscis, a. Ganglion, b. Inter- 

 space, d. Outer coat. c. Inner wall. e. Tubular band, with the nerve h. f. Mus- 

 cular bands, g. Suspensorium of the genitalia. C. Part of the female genitalia. 

 a. Ovary. 6 b. Ducts leading from ovary to uterus (spermiducts ?). c. Open mouth 

 of oviduct, d e. Uterus and vagina. 



XVIII. THE ANNELIDA. 



This is a class of large extent, containing the leech, the 

 earthworm, the Sipunculus, the lobworm, the seamouse and 

 Polynoe (Fig. 25), the Serpula, and the Spirorbis. 



All the members of this class possess a nervous system, 

 which consists of a longitudinal series of ganglia, situated along 

 one side of the body, and is traversed anteriorly by the 

 oesophagus ; the prse-oesophageal, or so-called " cerebral," ganglia 



* The investigations of Leuckart, while they demonstrate still more clearly the 

 close affinity which exists between the Acanthocephala and the Txniada by 

 proving the adult worm to arise by secondary growth within a hooked embryo, in 

 the former case as in the latter leave some doubt upon the nature of the reticu- 

 lated canals. According to Leuckart, they are the remains of the cavity which 

 primitively lies between the wall of the embryo and the contained rudiment of the 

 adult Acanthocephalan body. 



