482 



HISTOLOGY 



cells of the epidermis, extraordinarily developed and enlarged to make 

 a cocoon for the eggs. A considerable proportion of the body is com- 

 prised by these cells, and the 

 expenditure of the animal's 

 energy in secreting mucus must 

 be large. 



The secretion appears in 

 some of the cells in a dis- 

 solved state, and as solid 

 granules in others. It is used 

 both to make the cocoon and 

 to keep the body covered with 

 the slime that is always found 

 on its surface. The making 

 of the cocoon has never been 

 described or seen by the writ- 

 ers in this species, which was 

 taken from summer flounders 

 on the Massachusetts coast, 

 but it is undoubtedly done by 

 forming a shell of mucus in 

 the clitellar region around the 

 body, and then, after deposit- 

 ing the eggs and sperm, slip- 

 ping it off the body and at- 

 taching it as other leeches do. 

 The nidamental mucous 

 tissues of the earthworm are 

 to be found in an elevated, 

 band-like ring about the an- 

 terior part of the body, the 

 clitellum. Transverse sections 

 of this region show that mucus 

 is secreted, not from unicel- 

 lular glands as it is in the rest 

 of the animal's body, but 

 from closely set, tubular in- 

 vaginations in whose long 

 acini can be seen the large 

 mucus-forming cells (Fig. 

 453). The cells do not show a very clearly marked innate type at 

 the bottom of the fundus. For this reason, and also because their 

 nuclei show no degeneration process, it may be concluded that they 



1 1 



FIG. 453. Distal (A) and proximal (B) portions of 

 a single clitellar gland of the earthworm, Lumbri- 

 cus. X 780. 



