358 THE EARTHWORM CHAP. 



much wider, muscular part which opens on to the exterior 

 by the nephridiopore (Fig. 84). Sketch. 



VII. Remove a small piece of the integument containing 

 seta, and separate the latter out with needles. Mount in 

 water and examine. Sketch. 



C. Transverse Sections. For the preparation of these, 

 keep a worm for a few days in coffee-grounds or small pieces 

 of blotting-paper moistened with water, in order that the 

 gritty contents of its intestine may be replaced by a soft 

 substance which will not blunt the razor. Kill trie worm, 

 cut off a small piece about J inch in length from the region 

 of the intestine, and fix, stain, and cut into transverse 

 sections as directed on p. 136. Examine a section with the 

 low power, and note : 



1. a. The thin cuticle ; b. the epiderm, enclosing goblet- 

 cells (unicellular glands) ; c. the very thin derm; d. the 

 setce, with their sacs and muscles, if your section passes 

 through one or more of them. 



2. The muscles of the body -wall. a. The external circular 

 layer ; and b. the thicker longitudinal layer, appearing 

 feather-like in transverse section and broken up into bands 

 in the regions of the dorsal pores and setae. Note that the 

 muscles are unstriped. 



3. The ccelome and peritoneal membrane. 



4. The intestine, with its thick dorsal typhlosole. It is lined 

 by a single layer of columnar cells (enteric epithelium), 

 outside which is a thin muscular and connective -tissue 

 layer. Externally to this, again, are the elongated and 

 granular yellow cells, which are especially abundant in the 

 typhlosole. 



5. The dorsal, ventral, and intestinal blood-vessels. 



6. The ventral nerve-cord, just internal to the longitudinal 

 muscular layer. It is enclosed in a muscular and connective- 

 tissue sheath, embedded in which the sub-neural and lateral 

 neural vessels can be seen. Along the dorsal side are three 

 clear-looking " giant fibres." Observe the nerve-cells along 

 the cord ventrally and laterally, the nerves coming off from 

 the cord, and the symmetrical halves of which the cord is 

 composed. 



7. The nephridia : these will be seen cut through in 

 various planes. 



The thin septa will be cut through in different directions, 

 and their relations are therefore not easily seen in sections ; 

 note the circular and radial muscular fibres in them. Sketch 



