ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 219 



which contains the Platodes, Nemcrteans, and Rotifers, are only pro- 

 vided with cephalic ganglia and cerebral commissures ; the latter, 

 which contains Annelids, Gephyrea, and Nematohelminths, are pro- 

 vided with cephalic ganglia and a ventral ganglionic chain. The 

 nervous system of the last of these is stated by Gotte and Ganin to 

 consist of four rudiments, two dorsal and two ventral ; these very early 

 unite into a single ring. If this be so, the dorsal rudiments are 

 probably the homologues of the occipital plate, and the ventral rudiments 

 those of the ventral ganglionic chain. But the author acknowledges 

 that further researches are needed to demonstrate the legitimacy of the 

 systematic arrangement which he proposes to base on these embryo- 

 logical data. Sagitta has a still closer resemblance to Annelids and 

 Gephyrea, for the nervous system is formed of two rudiments, and there 

 is a true coelom ; in Nematodes the mesoderm does not become delaini- 

 nated into splanchnic and somatic layers, and only gives rise to the 

 longitudinal muscles. 



The unarmed Gephyrea diverge from the Annelid type of develop- 

 ment much more than do the armed Gephyrea ; in Sipunculw there is 

 only a rudiment of the pre-oral ciliated circlet, while in Phascolosoma 

 this is quite absent and the postoral circlet developes very early. 



Vascular System of Hirudinea.* — Dr. A. G. Bourne refers to M. 

 Jaquet's paper on the vascular system of Annelids. He regrets that 

 the author's interpretations tend to take us back to a condition of things 

 which existed forty years ago, and he ascribes this defect to M. Jaquet's 

 want of appreciation of comparatively recent work on the subject. • Dr. 

 Bourne makes some critical remarks on various genera of leeches which 

 have been incompletely described by M. Jaquet. 



Structure of the Eye of Branchiomma.t— M. C. Brunotte has 

 examined the structure of the eyes in Branchiomma, where, as is well 

 known, there is an eye at the tip of each of the branchial filaments. 

 The ocular mass does not completely surround the cartilaginous 

 axis of the branchia, there being towards the internal side a non- 

 pigmented zone covered by epithelial cells which are identical with 

 those on other parts of the gill. Examination in sea-water, aided by 

 pressure, reveals the presence of facets ; there is no difference in the 

 characters of the cuticle ; in sections each elementary eye is seen to 

 have the form of an elongated triangle, with its base turned towards the 

 periphery. Directly below the cuticle there is a small spherical lens, and 

 underneath it there is a nucleus of some size situated in a sort of rounded 

 cavity. The author compares the lens and cellular body with its large 

 nucleus to the crystalline formations of Arthropods ; the cell is inclosed 

 in a granular protoplasmic mass, in which an anterior, granular and 

 protoplasmic portion, in which there is another nucleus, may be distin- 

 guished from a hinder part which contains an elongated refractive body. 

 This last is regarded by M. Brunotte as the optic rod of the visual cell ; 

 its narrow internal end is continuous with nerve-filaments. There is no 

 trace of pigment in this region, but special pigment-cells surround each 

 of the elementary eyes. 



The author is of opinion that in Branchiomma we have to do with a 

 true compound eye, which differs from any which has yet been described 

 in Annelids. Grenacher and Carriere have always given the name of 



* Zool. Anzeig., xi. (18S8) pp. 1G-8. t Comptes Rendus, cvi. (1888) pp. 301-3. 



