i8o 



AN INTRODUCTION TO ZOOLOGY 



per. 



c.- 



the ventral nerve cord throughout almost its entire length, are 

 connected by means of fibrils with nerve cells in the ganglia 

 and probably distribute the impulse that causes a worm to con- 

 tract its entire body when strongly 

 stimulated (151). 



Sense Organs. The sensitive- 

 ness of Lumbricus to light and 

 other stimuli is due to the presence 

 of a great number of epidermal 

 sense organs. These are groups of 

 sense cells (Fig. 92, sn. c.) connected 

 with the central nervous system by 

 means of nerve fibers (nv.), and 

 communicating with the outside 

 world through sense hairs (per.) 

 which penetrate the cuticle. More 

 of these sense organs occur at the 

 anterior and posterior ends than in 

 any other region of the body (see 

 Fig. 90, 8). The epidermis of the 

 earthworm is also supplied with 

 efferent nerve fibers which penetrate 

 between the epidermal cells forming 

 a sub-epidermal network 1,144, 147)- 

 Reproduction. - - FEMALE OR- 

 GANS (Fig. 93). The female re- 

 FIG. 02. Tactile nerve endings in , . ,. 



the integument of the earth- Productive organs are a pair of 

 *orm. per., sensory hairs ovaries (0) in somite XIII, two ovi- 

 projecting through the cuti- ducts (OD) in somites XIII and XIV, 

 :le; nv., nerve ; sn. c., sense ari( l two pairs of seminal receptacles 

 (S) or spermathecce lying in somites 

 IX and X. The ovaries are small 

 pear-shaped bodies. They lie one on either side of the mid- 

 ventral line in somite XIII, and are attached by their larger 

 ends to the ventral part of the anterior septum. The oviducts 



cells. (From Dahlgren and 

 Kepner.) 



