ZooL.— Vol. II.] RISEN— OLIGOCH^TA. 99 



Studied. While Dr. Horst has found an increased number 

 of blood capillaries in the zone, I, on the contrary, find the 

 zone to be remarkably free from blood-vessels in the epi- 

 dermal layers. The long row of capillaries seen in Horst's 

 figure does not appear in my preparations, and there is 

 certainly nothing easier to demonstrate in an Oligochgeta 

 than blood-vessels, large or small. 



The caudal zone is characterized by the very narrow 

 segments of which it is composed. Any other portion of 

 the worm of an equal length contains only about half as 

 many segments as the zone itself. This further implies 

 that the zone contains about twice as many septa and twice 

 as many ner.ve-glanglia as any other portion of the body, 

 and is therefore stronger and more sensitive than any 

 other portion. 



The structure of the epidermis of the zone is quite inter- 

 esting. Horst and Beddard have commented upon the 

 absence of glandular goblet cells in the epidermis of the 

 zone, and Beddard has used this as an argument in favor of 

 his theory of regeneration and growth. Horst (17) has 

 pointed out that the absence of goblet cells and the presence 

 of columnar epithelial cells makes a structure different from 

 that which we would expect to find in a zone of growth, — 

 such a one as is found in Nais, Chcetogaster, Lumhricuhis, 

 etc., — and that there is, in fact, no trace of any embryonic or 

 primitive features in the zone. If to this is added the fact 

 that the zone is most regular in the size and number of its 

 somites, it appears as though very little remains to indicate 

 that it is a zone of growth and regeneration. 



If the histological structure of the epithelium of a seg- 

 ment of the zone is considered, it is found to consist of two 

 distinct structures : one of these borders the intersegmental 

 groove and is composed of uniform, large and regular sup- 

 porting cells with large ovoid nuclei; the other occupies the 

 larger portion of the epidermis and lines the outer convex 

 part of the somite; it contains comparatively few support- 

 ing cells, but has a large number of cells of a different 

 nature. In fig. 21 I have endeavored to illustrate this; 



