ZOOLOGY AND BOTANY, MICEOSCOPY, ETC. 



25 



more the secreting cells of the foot-gland. The constituent cells are 

 surrounded by membrane, and lie in a network of connective tissue. 

 It would seem probable that the investing membrane is continuous 

 with the walls of an efferent duct. Histological investigation does 

 not, therefore, speak in favour of this organ having a sensory func- 

 tion, and it does point very distinctly to its glandular nature. 



The third organ in dispute — the foot-gland — is looked upon by 

 the author as being the olfactory organ. It is well supplied with 

 nerves, and is of some size. It consists of oval cells, set in the spaces 

 formed by the crossings of muscular fibres, and is placed in the middle 

 line of the foot. The gland is surrounded by two or three circular 

 vessels. The cells are arranged in groups and imbedded in a net- 

 work of connective tissue fibres. They vary in form, have granular 

 contents, and the nucleus has an eccentric nucleolus. There is an 

 efferent duct for the gland, and the intermediate duct has its walls 

 formed by epithelial cells of two kinds. Most are flattened and 

 cylindrical, and when placed near the cleft in the gland are provided 

 with cilia. The deeper layers contain oval cells, which give off near 

 their surface a delicate rod, which enlarges at its free end into a short 

 ciliated knob, so that they have a close resemblance to the neural cells 

 detected by Flemming in his investigations into the sensory organs of 

 the Mollusca. It results from this that we find in the interior of the 

 body a glandular body communicating with the exterior, in which there 

 are to be detected cells which resemble the sensory cells found in the 

 integument of the Mollusca, and to which, therefore, we should ascribe 

 a sensory function. To determine the function of an organ thus 

 situated would be a matter, perhaps, impossible, and certainly of very 

 great difficulty. That that function is sensory is spoken to by the 

 following considerations : — The three necessary factors of an olfactory 

 organ — the presence of a layer of sensory cells, the entrance of air, 

 and the addition of a secretion from a glandular organ — are here all 

 present ; the orifice at the anterior margin allows the air to enter ; the 

 olfactive matters contained in it are mixed with the secretion, and so 

 come into contact with the peripheral nerve-cells. The author con- 

 cludes by pointing out that the sensory arrangements which obtain in 

 the Invertebrata are not to be compared too critically or hastily with 

 those which are seen in the Vertebrata. 



Embryo of Planorbis.* — The publication of Fol's researches f 

 induced Herr C. Eabl to repeat his former observations on the embryo- 

 geny of Planorhis.X As touching all points mooted between himself 

 and Fol, Eabl would maintain his previous statements in their 

 entirety. He desires, however, to extend and correct his earlier re- 

 sults on two matters of detail, not in dispute between himself and the 

 Genevese observer. 



1. The first of these concerns Lankester's assertion that the 

 orifice of invagination " closes up, and the pedicle so formed becomes 

 the rectum." This had already been disputed by Eabl, who now 



* Morph. Jahrb, (Gegenbaur), vi. (18S0) pp. 571-80 (1 pi.), 

 t See tliis Journal, iii. (1880) p. 605. X Ibid., p. 235. 



