180 MR W. E. HOYLE ON 



With regard to the function of this cell-system, I have, as will be inferred 

 from what has just been stated, no theory to offer; if it be really a portion of 

 the hook-gland, then the suggestions of Leuckart seem the most apt that can 

 be offered, and if not, the discovery of the destination of the secretion must 

 precede any further hypothesis. 



3. The Stigmatic Cell-groups (P1."XXVII. figs. 9 and 11, s.c) have been 

 already alluded to as situated immediately within the stigmata. They are 

 spheroidal in form, and their inner surface projects only a little beyond that of 

 the subcuticular epithelium, so that they have an average diameter of about 

 02 mm. They are not very transparent, and take up the straining material 

 eagerly, so that their structure is somewhat difficult to make out. Each con- 

 sists of from six to nine small cells, with clear or clouded protoplasmic contents, 

 and a comparatively large variously-shaped nucleus. The outer aspect is 

 moulded into a kind of short neck which lies within the stigma, and is closed 

 by a fine very darkly stained line. 



Such being the appearance of these structures, it becomes necessary to 

 inquire into their homology and function. In Leuckart's classic # work there 

 are described in the earlier developmental stages of L. twnioides vesicles of 

 clear fluid in relation with the stigmata, and these in the adult are replaced by 

 large cellular processes which project into the body-cavity. It would seem, 

 then, that we have in the subject of the present investigation a condition inter- 

 mediate between the two just described, and this is rendered more probable 

 inasmuch as Leuckart speaks of and figures an incipient segmentation. 



These cell-groups are possibly homologous with the subcuticular glands 

 described by Kolliker in certain insects ;t it is scai'cely possible that they have 

 any relation other than a merely analogical one with glands, which they closely 

 resemble in structure, described by Andreae in Sipunculus nudus.% 



With respect to the function discharged by these structures it seems quite 

 possible that they take part in the formation of the cyst which encloses the 

 animals, unless they be excretory in nature, and destined only to come into 

 full activity on the further development of the animal ; it is not impossible, 

 however, that both these suggestions may be true. 



The Nervous System. 



As might have been anticipated, the nervous system of the subject of this 

 paper shows but slight differences from that of any similar forms which have 

 hitherto been examined. It consists of a single median ganglion, showing, 

 however, traces of a primitive division into two lateral halves, and of about 



* Loe. cit., p. 33. 



t Verhandl. d. phys. med. Vero'ns Wiirzlmrg, p. 76, 1857. 



% Z itschr.f. iviss. Zool., Bd. xxxvi. p. 201, Taf. xii., figs. 1 and 4, 1881. 



