218 Descriptio7i of the Plates. 



h I. First and second pairs of sub-oesophageal ganglia, very 

 closely apposed to each other. From the first siib-oeso- 

 phageal ganglion, five pairs of nerves are given ofi"; from 

 the second only two, as from all the other twenty ganglia 

 placed posteriorly to it, with the exception of the two last. 



b 2. Last ganglion, the twenty-second of the ventral chain. 

 This ganglion gives ofi" from five to nine pairs of nerves, 

 which are distributed to the posterior sucker. The penulti- 

 mate ganglion gives off only one pair of nerves. The supra- 

 oesophageal ganglion, with the three stomato-gastric gang- 

 lia connected with it and supplying the jaws, is not shown 

 here; nor the azygos sympathetic nerves with a course 

 above the ventral nerve-chain, and between it and the 

 digestive tract upon which it forms gangliated plexuses, 

 and sends branches along its lateral diverticula. 



CI. First lateral diverticulum of the portion of the digestive 

 tract, which comes next after the pharynx, and which is 

 called ' oesophageal^ by Gratiolet, inasmuch as its functions 

 are, according to him, merely those of a reservoir for the 

 more solid parts of the animals food, from which the watery 

 part is squeezed out by the muscular contractions of the 

 body-walls whilst it is contained there ; and which, after 

 remaining there thus condensed for several months, still 

 retains the faculty of reddening, when exposed to the 

 oxygen of the air. 



C2. 'Small intestine' of most authors, 'gastroileaF portion of 

 digestive tube of Gratiolet, in which the blood undergoes 

 the alterations ordinarily effected in it by digestion. It 

 ends posteriorly in a short ovoidal colon, which again ends 

 in a short rectum, which turns slightly upwards to end at 

 the anus. The small intestine is a little dilated at its 

 commencement in the interval between the two terminal 

 sacculi c 3 ; this dilatation representing the much larger 

 bilobed dilatation, with which the homologous segment of 

 the digestive tract commences in the Horse-leech {Aidostoma 

 Gulo) . 



C3. Eleventh lateral diverticulum of right side prolonged down- 

 wards on either side of the small intestine and colon, as far 

 as the point where the rectum begins. The calibre of either 



