ON DIPLOZOON XIPPONICUM, X. SP. 163 



specimens with fully develojjed vitelline body, these muscles are 

 obscured to a g^reat extent. 



III. The Organs of Attachment. 



The organs of attachment are constituted, posteriorly by the 

 four pairs of suckers already mentioned and a pair of hooks, and 

 anteriorly by a pair of suckers and sticky glands. Each posterior 

 sucker (Figs. 3, 4, 5) may Ijrieüy be described as a short-ovate, flat 

 bag with its wide mouth directed ventrally, its walls very thick, and 

 the line of its greatest breadth directed transversel}^ to the long axis 

 of the body ; so that we may speak of the anterior (aw), posterior 

 (pw), and lateral walls. The first two walls are very thick, and are 

 directly continuous with each other at the bottom of the bag 

 (Figs. 4, 5). The lateral walls are very thin, and seem to consist of 

 a cuticula-like refractive membrane only. The entire structure is sup- 

 ported by a framework of chitinous rods, which are by no means 

 so numerous or complicated as Nordmann has represented them. 

 They are five in number : a U-shaped median piece (pm), a pair of 

 curved pieces (ppa), (resemliling in form certain fishing-hooks), to 

 support the anterior wall, and a pair of simihu- pieces (ppp), with a 

 large process ([)p) at the base, to support the p(rsterior wall. Having 

 thus given a general idea, I shall now proceed to the explanation of 

 the three figures already referred to, by which I hope to make clear 

 the structure of the suckers. Fig. 3 represents the chitinous rods as 

 very commonly seen in a specimen observed under the pressure of a 

 cover-glass, with the mouth of the sucker directed below in the figiu'e 

 and the rods belonging to the anterior wall shaded more deeply. 

 Fig. 4 represents a section made in the direction indicated by the 

 line ab in Fig. 3, whereby it is to be remarked that the median 



