ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 737 



and those for the photogenic function. The former, however, is provokeil 

 by luminous vibrations from without, while the latter has, as its final 

 result, the emission of luminous radiations into the surroumliug medium. 



Nudibranchiate Mollusca of Plymouth Sound.*— Mr. W. Garstang 

 enumerates twenty-four genera and thirty- six species of nudibranchiate 

 Mollusca from Plymouth Sound. Among the valuable captures are two 

 examples of Idalia aspersa and three of Lomanotus. The author has 

 endeavoured to furnish facts regarding the life-conditions of this group. 

 Evidence is rapidly accumulating to prove that, in it, colour, whether 

 Cf;nspicuous or dull, has a very important value for the individual and 

 tbe sj ecies. Some cases of wliat appear to be mimicry are reported. 

 AVith regard to the bright colours of the papillae of Aeolids the author 

 suggests that, in addition to tlieir main purpose of warning enemies of 

 the presence of disagreeable qualities (e. g. nematocysts), there is another. 

 The bright colours are confined to the pipillag which can bo detached 

 from the body with the greatest ease and are reformed to their full size 

 in two or three days ; this arrangement must be serviceable in directing 

 the experimental attacks of young and inexperienced enemies to the non- 

 vital papillae, and away from the vital, inconspicuously coloured parts of 

 the body. 



Microscopic Anatomy of Dentalium.t — Prof. H. Fol considers that a 

 genus which represents by itself a class of the Animal Kingdom always 

 deserves close study, but we cannot, we fear, give him all the space 

 which his detailed monograph demands. 



The ectoderm forms a simple epithelium over all the free surface of 

 Dentalium, but the thickness of the layer varies in difterent regions and 

 with the condition of retraction or extension in which the parts are 

 found; the cells are in some parts flattened, and in others cylindrical. 

 As in Lamellibranchs, there are a number of cutaneous glands, all of 

 which are unicellular, and of which there are two types, which are 

 respectively distinguished as the hyaline and the granular glands. 



It is probable that the glandular tissue jjlays a part in the formation 

 of the shell, but this may not be its only function. All the ectoderm 

 except that covered by the shell is ciliated. The epithelium of the 

 digestive tract forms a single layer which is comparatively deep, for the 

 cells are elongated in the perpendicular direction ; some of the cells are 

 ciliated and some glanclu'ar, but it is probable that all are ciliated when 

 young. The ciliated cells present ;in interesting peculiarity which the 

 author believes to be very common in the Animal Kingdom, though not so 

 well marked as in Dentalium. The cilia are implanted in a layer which 

 is more transparent than the subjacent part of the cell ; when this trans- 

 parent layer is closely examined, it is seen to be crossed by pale lines 

 which appear to cori-espond exactly to the cilia. In the middle of each 

 of these striae there is to be seen, in preparations which have been 

 treated with carmine after Grenacher's method, a small corpuscle 

 coloured a deep red like the nucleus. Finally, the part of the cell which 

 is situated between the nucleus and the transparent layer is traversed by 

 strife almost perpendicular to the surface, which seem to have a relation 

 to the cilia. The author gives some details as to the structure of the 

 radula and the parts connected with it. The liver is a collection of caeca 



* Journ. Marine Biol. Assoc, i. (1889) pp. 173-98. 

 t Arch. /loI. Exper. et f4o'n., vii. (1889) pp. 91-148 (4 pLo.). 

 1889. 3 F 



