Annulata. 53 



The kidneys open to the outside usually between the inner and 

 outer rows of bristles, but sometimes above the lateral row of 

 bristles. And each tube kidney begins as a funnel, which is in 

 the segment in front of the one in which the loops of the kidney 

 are found. 



17. The outer layer of the skin is thin and easily peels off. 

 This is the cuticle, and is noticeable on account of its pearly luster. 

 The bulk of the body wall is composed of two layers of muscles, 

 the outer of circular and the inner of longitudinal fibers, by means 

 of which the worm moves. 



1 8. In a freshly opened earthworm mount a drop of the milky 

 liquid found in the body cavity and examine it under a one-sixth 

 objective. The corpuscles should be distinctly seen. 



CROSS SECTION OF AN EARTHWORM (MICROSCOPIC). 



1. Examine cross sections: under the microscope, with a low 

 power, one-half or two-thirds inch objective. The body wall may 

 be seen to consist of several layers. The intestine has an extension, 

 the typhlosole, from its dorsal wall, occupying considerable of the 

 space within, and adding much to the inner surface of the intestine. 



2. Examine with a higher power, one-fourth or one-sixth inch 

 objective. There are five layers of the body wall : (a) the thin 

 cuticle ; () a thicker layer of skin, the hypodermis, or epidermis, 

 which produces the mucus which coats the outside of the worm ; 

 (c] the layer of circular muscle fibers; (d) a thicker layer of 

 longitudinal muscle fibers ; (<?) a very thin layer of peritoneal 

 epithelium. 



3. The dorsal blood tube lies embedded in cells on the dorsal wall 

 of the intestine. Under the intestine is the ventral blood tube. Still 

 lower is the nerve cord, or ganglion, as the section may strike. 



Read The Formation of Vegetable Mold through the Action 

 of Earthworms, Darwin ; or the chapters on the earthworm in 

 General Biology, Sedgwick and Wilson. 



Topics for Reports. Varieties of Earthworms. Marine Worms. 

 Leeches. 



