178 MR W. E. HOYLE ON 



structures as van Beneden described in his P. Diesint, V' arid" as those to which 

 Leuckakt alludes in P. cyli/ulricum, P. oxycephalum, &c.f They are elongated 

 bolster-shaped bodies, tapering slightly towards either end and flattened on the 

 median surface which is in relation with the intestine (PI. XXVII. fig. 10, h.g). 

 They extend forwards into the head, but about the point where the oesophagus 

 opens into it they leave the intestine, and passing outwards unite with the 

 body-wall ; posteriorly they extend to within a few millimetres of the hinder 

 extremity of the body. 



Their length is thus very little less than that of the entire animal, while 

 their average diameter is about - 7 mm., so that they fill up the greater part of 

 the body-cavity on either side of the intestine. 



Each gland is covered by a delicate membrane, and within is made up of 

 very large cells varying 0'07 mm. to 01 5 mm. in diameter, of very diversified 

 shapes and packed closely together. 



The cells were found to contain a coarsely granular protoplasm, and a 

 large nucleus (0*02 mm. in diameter) in which a nucleolus could only very rarely 

 be distinguished. 



In the centre of the gland may be seen the duct (fig. 10, h.g'), a tube 0*02 mm. 

 in diameter, with a lumen of O'OOS mm., lined with a very delicate layer of 

 chitin. This duct was traced forwards through a series of transverse sections 

 nearly as far as the bases of the hooks ; beyond this point, however, it could not 

 be followed ; but there can be no reasonable doubt that it opens in the invagina- 

 tion of the cuticle in which the hook is situated, as described by Leuckart. I 

 could detect no ducts passing towards the mouth, but only the two pairs pro- 

 ceeding in the direction of the hooks ; neither the duct nor any portion of the 

 gland passes through the nerve ring, as in P. oxyce$)haliim.\ 



These glands would seem from their position and relations to be homologous 

 with the salivary glands of other Arthropoda ; the fact of their opening at the 

 base of the appendages and not into the cavity of the mouth might be an 

 obstacle to the adoption of this view, unless perhaps these are to be regarded 

 as homologous with the jaws rather than with the limbs of allied forms. 



2. The Parietal Cells (PI, XXVII. fig. 9, p.n) I propose for the present to 

 term a number of large oval cells scattered in the mesoderm of the body-wall, 

 because at present no opinion can be offered as to their function. They consti- 

 tute one of the most conspicuous characters seen in the examination of sections, 

 both longitudinal and transverse. 



In form they are ovoid, generally flattened by mutual contact, and averaging 

 03 mm. in diameter ; they contain a deeply stained spheroidal nucleus of 



* Ann. d. Sci. Nat., ser. 3, t. xi. p. 324, 1849. 

 f Letjokart, he. cit., p. 67. 

 \ hoc. cit., p. 67. 



