ZOOLOGY AND BOTANY, MICBOSCOPY, ETC. 61 



fibrils ganglionic cells are scattered irregularly, and they are remark- 

 able for the small quantity of protoplasm whicb surrounds the nucleus. 

 While the pyramidal feet have not, the sucking feet have a sucking 

 plate, the epidermis of which consists of elongated cells of palisade- 

 like form ; these pass into the circular ridge, the cells of which are 

 much shorter and of two kinds ; some are cylindrical and connected 

 by fine fibrils with a layer which appears to be nervous, while others 

 have stout processes, which pass perpendicularly through the nervous 

 layer and become united with the subjacent connective tissue. 



In each of the shield-shaped tentacles around the mouth we find 

 that the stalk has a canal which gives off branches to each of the 

 " capitula " which form the free end. The epithelial layer of these 

 capitula is worth study ; the cells are filamentous and give off pro- 

 cesses which are of two kinds, some being stronger than the others 

 and not forming a plexus. In longitudinal sections we see a layer 

 underlying the epithelium, which is in parts finely granulated, and in 

 parts striated ; the epithelial supporting cells terminate beneath the 

 fibrillar layer, while the separate fibrils of the epithelial sensory cells 

 are continued into the nerve-cord of the epithelium, which again is a 

 branch from the large nerve-trunk in the stalk of the tentacle. 



The Cuvierian organs are next dealt with, and are described as 

 tubular structures, beneath the ciliated epithelial layer of which is a 

 peculiar striation ; this consists of strongly projecting bands arranged 

 circularly and parallel to one another, and have glandular cells, in 

 rows, among them. Longitudinal and circular muscles are also to be 

 observed. In the centre of ejected tubes there appears to be a canal, 

 but this may be due to the breaking up of those structures, and fresh 

 material must be examined before any certain conclusion as to its 

 normal presence can be arrived at. 



The circular nerve-cord of Synapta presents the following histo- 

 logical characters : the greater part of it is formed by circular fibrils, 

 the nerve-fibres, among which cells are irregularly scattered ; this 

 nerve-layer proper is traversed by processes, which arise from the cells 

 that form the superficial layer, and which, with their processes, may 

 be regarded as supporting epithelial cells ; they are homologous with 

 the similarly named structures found in the epidermis of Asterids. 



From the nerve-ring there are given off five radial nerves ; these 

 are set in the layer of connective substance, below them there is a 

 vessel, then the circular, and then the radial muscles. The nerve-trunk 

 is divided into two parts and probably also supported by a thin cord 

 derived from the connective tissue. The radial nerve gives off 

 fibrous bands, which supply the circular muscles, and others which 

 pass to the periphery of the body and end in the tactile papillae. 

 These latter appear to be developed in consequence of the loss of the 

 suckers or feet ; they present the following structures : the epithelium 

 is greatly thickened, and its cells are cylindrical and two or three 

 times the length of an ordinary epithelial cell ; nerve-fibres pass into 

 them. In addition to these ordinary papillsB, there are others which 

 inclose calcareous bodies, and especially those anchor-like structures 

 which are so characteristic of the group ; in these no nerve-fibres 



