35 THE EARTHWORM CHAP. 



Kill the worm, cut a small piece about 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 (unicel- 

 lular glands) ; c. the very thin derm ; d. the seta, 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 

 setne. Note that the muscles are unstriped. 



3. The ccelome and peritoneal membrane. 



4. The intestine, with its thick dorsal typhlosolt. 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, im- 

 bedded 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 mphridia : 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 the lateral half of your 

 section, and then put on the high power and work through 1-7 again. 

 Notice that the cavities in the sections of the nephridia are intra- 

 cellular, except in the muscular part. Sketch as many details as 

 possible. 



(If time permits, prepare and examine a series of transverse sections 

 through the genital region, and observe any important points not 

 already made out in your dissection. Note especially the spermaries 

 and spermiducts}. 



