482 JOSEPH STAFFORD, 



the form of a large sack extending through the centre of the upper 

 portion of the body and ending blindly at about the middle of the 

 posterior third of the animal. 



At first the indentation between neck and foot is but a trans- 

 verse slit (Fig. 7) but as it deepens it narrows into a pit — the 

 cervico-pedal pit — of which the boundary walls are: above, the 

 ventral wall of the neck ; below, the dorsal wall of the anterior pro- 

 jection of the foot; at the sides, muscular walls connecting these two. 

 Continuous with the inferior wall of the neck, passes backwards, 

 through the animal , a broad , horizontal , muscular partition , the 

 diaphragm (Fig. 3, 7, 2, 11, 12), or septum, which is concave above, 

 joins the side walls of the body, and extends to the distal end of the 

 intestine. This divides the worm into an upper and a lower division 

 which are continuous with one another round the posterior end of 

 the intestine. In the supra-septal portion, on each side, between the 

 intestine and the body walls, are the vitellaria (Fig. 11, 12); and 

 anteriorly , converging towards the middle line , are the end-organs 

 (Fig. 16, 9, 3, 2, 7) of the genital system, opening, by means of a 

 common genital pore, into the cervico-pedal pit. In the infra-septal 

 portion are situated: more anteriorly, the ovary (Fig. 3, 11, 12, 16), 

 with the oviduct passing backwards round the end of the septum and 

 intestine and then forwards to the porus genitalis; more posteriorly, 

 but still near the centre of the animal, the testis, with its much shorter 

 conducting tube passing upwards and forwards through the diaphragm 

 to meet with the corresponding female organ at the genital sinus. 



These organs, with their accessory parts, all lie suspended in a 

 parenchyma tissue (Fig. 1, 2, 7) which fills the si)ace between them 

 and the outer integument of the worm, and which also carries nerves 

 and excretory tubules. 



Below the infra-septal portion, and separated from it by a limiting 

 membrane, is the ventral sucker (Fig. 3, 7, 2, 11, 12, 13) composed 

 of four longitudinal rows of ventrally hollowed quadrangular fields. 

 Infra-septal portion and sucking disk form the foot. 



From these general views I shall now turn to a description of 

 the organs in detail. 



^ Integumentary system. 



Cuticle. Investing membrane. Everywhere the surface 

 of the body is covered with a thin cuticle (Fig. 1, 7) which is also 

 continued into the external openings of inner organs. It is reflected 



