548 John Beard 



Auatomy and Histology. 



Although it ìs not my intention to euter fully into the anatomy and 

 histology of the adult, nor indeed is such a task necessary, for Semper ^ 

 aud Graffa have both studied it with great exactness aud detail, still 

 there are some points in which I am able to add to our knowledge under 

 this head. These ehiefly concern the nervous system, sense organs, and 

 alimentary canal. 



Skin and Sense organs. 



As is already well knowu the skin of Myzosioma is made up of a 

 cuticle underlyiug which is a layer of cyliudrical ciliated epithelium. 

 This cyliudrical epithelium is composed of cells the bases of which do 

 not rest on a basemeut membrane, but are prolonged into processes 

 which Stretch into the subl^dug cutis fig. 32) . 



Whether they are there connected with nerve ganglion cells or not, 

 as Flemming has described in Molluscs, I have not been able to deter- 

 mine, but hold it for probable. 



Fig. 32 is a camera lucida drawing under '/^ in. Homogeneous Im- 

 mersion. In the other figures in the piate the epidermis is represented 

 somewhat diagrammatically as if it were composed of cells which are 

 cyliudrical along their whole length. 



The nuclei of these epithelial cells are prett}^ large and roiinded, and 

 stain deeply. When a well preserved section of the epidermis is exa- 

 mined under very high power, such as that of au ^/ !§ in. Hom. Immer- 

 sion, the protoplasm of the celi is seen to be finely striated, the Striae 

 passing from the nucleus to the external surface fig. 32). This striation 

 is the optical expression of fine protoplasmic threads, which are in- 

 deed the cilia, or rather direct processes of them. Thus the cilia pass 

 through part of the protoplasm of the celi, and are directly connected 

 with the nucleus '^. 



In fig. 31 which is part of a section of the skin certain curious rods 

 are seen , these I take to be a sort of sense organ, probably of touch. 

 The preparation is from au animai killed aud stained with osmic acid. 

 It is seen that these sense organs consist of short spindle-shaped rods of 

 considerable length. They are composed of chitin. and show a double 

 contour, and hence are hollow. They are set directly on the cuticula, not 



1 1. e. 2 1. e. 



3 These fine Striae are not well shown in the fiorare. 



