236 NIERSTRASSIA FRAGILE. 



depression provided with long cilia (Plate 6, fig. 8), lying behind the mouth 

 or atrial opening from which it appears in surface views to be separated by a 

 very narrow cuticular bridge continuous with the general investment of the 

 body. The gland itself, occupying the visceral cavity halfway up the sides 

 of the body, extends from the anterior end of the animal to a point about level 

 with the posterior end of the radula. The cells composing it are pyriform, filled 

 with a darkly staining secretion, among which are larger, lavendar colored 

 masses, apparently consisting of more than one cell. This may be one stage 

 of glandular activity though it appears to be a different secretion. 



The foot (Plate 7, fig. 1) arises immediately behind the outlet of the anterior 

 gland in the form of a single fold that, accompanied by the usual pyriform gland 

 cells, extends to a point a short distance in front of the cloacal opening. 



The mouth opening is, as usual, subterminal in position (Plate 6, fig. 3), 

 and in some specimens is reduced to a very small pore scarcely larger than in 

 some species of Chaetoderma, while in other cases it is more or less open. In 

 any event it leads into a small chamber holding the position usually occupied 

 by the atrium, but it is somewhat doubtful if it should be interpreted as such. 

 So far as can be detected after careful examination there is no trace whatever 

 of any cirri or atrial ridges, and as the cells Uning this space are in large measure 

 at least clearly modifications of those present in the undoubted oesophagus or 

 pharynx it would appear that the atrial chamber is wholly wanting. On the 

 other hand it is important to note that the usual nerves passing out from the 

 forward surface of the brain connect with masses of ganglion cells, probably 

 the homologue of those about the bases of the cirri in other species, and from 

 these masses fibres may be distinctly followed to the bases of some of the cells 

 Uning the cavity in question. According to the nerve supply the atrium exists, 

 but judging from cell characters alone it is absent. On which of these criteria 

 dependence is to be placed it is difficult to say though personally I am inclined 

 to take the first named position. 



As may be seen (Plate 6, fig. 9) the cells of this first section of the canal are 

 of two, possibly three distinct varieties, club-shaped elements, usually long 

 and slender especially on the dorsal surface, and thread-Hke supporting or sense 

 cells. In the first type the distal portion is almost wholly occupied in pre- 

 served material by a vacuole, the nucleus occupying the basal section. The 

 supporting or sensory cells Ukewise usually possess basal nuclei, but especially 

 near the antero-dorsal boundary of the cavity some are more distally situated. 

 Often the free surfaces of all of these cells are covered with a yellomsh brown, 



