VERMES. 15 



The animal has been laid open along the ventral surface, 

 the nervous system having been removed. 



The mouth, into which a black bristle has been inserted, 

 leads into a thick, cylindrical, muscular sac, called by some a 

 gizzard. The posterior extremity of this opens by a narrow, 

 sigmoid segment, into a funnel-shaped stomach, which gradually 

 diminishes in size, and insensibly passes into an intestine, ter- 

 minating at the anus. Throughout the whole length of the 

 stomach, caecal processes are given off on each side to the 

 number of about twenty pairs. They are slender at their 

 origin, but gradually enlarge, and give off lateral ' diverticula,' 

 which again, in their turn, divide and subdivide, terminating 

 finally in fusiform dilatations. These caeca are probably homo- 

 logous with the gastric caeca of the leech ; and the so-called 

 * gizzard,' which is capable of protrusion, has been considered to 

 be homologous with the projectile proboscis of other Annelids. 



The stomach has been filled with red injection, and the 

 caeca partially so. They have been dissected and pinned out on 

 the left side. On the right they remain in situ, lying among 

 the transverse muscles. On this side also may be seen the 

 delicate muscular bands, which pass from the base of the 

 bundles of setae to the integument, and effect their protrusion. 



25. The same, dissected to shew the ' elytra/ 



A longitudinal strip of the dorsal coating of ' felt ' has been 

 removed and the ' elytra ' displayed. 



The 'elytra' are broad membranous plates developed as 

 appendages from the notopodia, and, arching inwards over the 

 back, form two lateral series on either side of the medio-dorsal 

 line. Beneath the elytra is the membranous partition forming 

 the dorsal boundary of the visceral cavity. The nervous sys- 

 tem may be seen on the ventral surface of the body, through 

 the integument. 



It is to be observed that the ' Sea Mouse ' is much less dis- 

 tinctly annulated than the Earthworm : and that the ' setae,' 

 which in the Earthworm are almost microscopic, are here of 

 large size and iridescent. 



26. A Leech (Hirudo medicinalis), dissected to shew its 

 nervous and generative systems. 



The nervous system consists of a longitudinal ganglionated 



