ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 775 



Hyalina, Vitrina). The median lateral plates are really only 

 transitional between the internal and external laterals, and are only 

 occasionally characteristic. The external lateral plates are of most 

 use, not only in distinguishing genera, but groups. For specific 

 diagnosis all the four groups of teeth must be noted. The following 

 provisional grouping is suggested : — 



I. Internal lateral plates with a median lateral tooth. 



(a) The outer lateral plates hook-like and very long ; the 



cutting edge untoothed (Limax, Hyalina). 



(b) The outer lateral plates hook-like and short ; the cutting 

 edge toothed ( Vitrina). 



II. The internal lateral plates icithout lateral tooth. 



(a) The external lateral plates are long-stalked (Succinea). 



(b) The external lateral plates are lamella-like and toothed 



on their posterior margin (Helix, Avion). 



Histological Structure of the Dorsal Papillae of Onchidium.* — 

 This preliminary report, by Dr. E. v. Lendenfeld, is founded on 

 sections through specimens of Onchidium chameleon Brazier, and 

 0, Ddmelii Semper. ' 



O. chameleon has small papillae and no eyes, whilst 0. Danielii 

 has three eyes on each papilla. The author corroborates Semper's 

 account of the eye : the character of the epithelium of the tubercles 

 is identical in the two species. The eyes multiply by division ; 

 semi-detached eyes with two lenses, but with one pigment layer, are 

 not unfrequent. The lens consists of a single cell, capable of dividing ; 

 the retina is more complicated than is described by Semper. Below 

 the ganglia-cells of the optic nerve are cells containing highly 

 refractive plano-concave bodies. Below these cells are elongated 

 hexagonal cells with pigment-cells at the sides of them ; a concave 

 space is formed at the bottom of each hexagonal cell, and in this space 

 is a conical rod, attached by its broad base to the bottom of the concave 

 space, and tapering gradually to a fine point, which is continued as 

 a fine thread through the centre of the hexagonal cell, and enters the 

 ganglia-cell layer. 0. Ddmelii never retracts its tubercles, however 

 near the forceps, &c, approach. " This might lead one to assume 

 that this animal is far-sighted." The concave lenses at the upper 

 ends of the facets, below the large spherical lens, are secondary, and 

 are produced in order to counteract the excessive power of the main 

 lens in the air ; although this latter would be well adapted for use in 

 the water. 



Development of the Gill in Fasciolaria.t — Eeserving a detailed 

 description of the complete development of Fasciolaria tulipa for a 

 later paper, Dr. H. L. Osborn describes the development of the gill 

 only, an abstract of the paper having been already given,! when the 

 Gastropod was called, improperly, Neptunea. 



The surface views were taken from living specimens, which were 



* Proc. Liun. Soc. N. S. Wales, x. (1886) pp. 730-2. 



t Stud. Biol. Laborat. Johns-Hopkins Univ., iii. (18S6) pp. 219-24 (1 pi.). 



X See this Journal, v. (1885) p. 226. 



