130 Descriptions of Preparations. 



lateral diverticula are eleven in number, the two anterior being 

 smaller than the nine succeeding- ones, and differing from thera 

 also in not having their outer angles prolonged backwards. The 

 last pair of diverticula are twice the length of any other pair, and 

 bending sharply back almost immediately at their commencement, 

 so as to become apposed to each other along the middle line, are 

 prolonged backwards up to a point on a level with the commence- 

 ment of the rectum, and nearly up to the termination of the body. 

 The digestive tube is of very small calibre posteriorly to the point 

 of origin of the two last diverticula, and lies in the interval 

 between them superiorly. The diverticulate portion of the di- 

 gestive tract is called a ' stomach'' by most writers, but it is 

 considered to be homologous and analogous with a crop or dilated 

 oesophagus by Gratiolet, on account of its resemblance to the crop 

 of the Horse-leech {Aulostoma gulo), and on account of its functions, 

 which appear to be merely the squeezing out the watery part of 

 the blood which the animal swallows, and allowing it to be dis- 

 charged by the segmental organs. Dissepiments run transversely 

 across the body, and interpose themselves between the apposed 

 walls of the several diverticula. The central emargination in each 

 of the septa thus formed, corresponds to what was the antero- 

 posterior part of the digestive tube in the region of the diverticula; 

 the method of preparation has given the shape of an ellipse to 

 what was, in the natural state of the parts, a circular foramen in a 

 diaphragm. A rudimentary dissepiment passes off from the pos- 

 terior aspect of each of the eight larger dissepiments, inwards and 

 backwards, within the cavity of each diverticulum towards the 

 middle Hne ; but it is not prolonged quite up to the line of the 

 chain of nerve-ganglia. An accessory compartment is thus added 

 on to each of the diverticula from the third to the tenth inclu- 

 sively; whilst the eleventh pair has five pairs of accessory im- 

 perfect dissepiments, introdigitating along their interior. The 

 ganglia of the ventral chain are seen towards the posterior part of 

 each compartment, constituted by the median portion of the di- 

 gestive and its lateral appendages ; and in some cases they are in 

 immediate relation with the anterior face of the dissepimental wall. 

 A black bristle has been introduced into the segments of the di- 

 gestive tract, posteriorly to the point where the last diverticula 

 are given off. The ' oesophagear portion of the tract projects and 



