ON MONOPYLEPHORUS LIMOSÜS. 



often in segments XI-XIII or JX-JXIII, and is 4-5 times as thick 

 as the extra-clitellar hypodermis. The clitellum is thinner on the 

 ventral side than on the dorsal and shows a break at two points 

 in the ventral median A cv 



line of the body : one 

 at the male pore and the 

 other at the fnrrow cor- 

 responding to septnm 

 XI/XII. 



The clitellum con- 

 sists of regularly arrang- 

 ed, large gland cells and 

 strongly compressed sup- 

 porting cells (fig. 2, B). 

 The clitellar gland cells 

 are generally 25-30 p. 

 long and 4-6 p across 

 in the dorsal region, 

 while in the ventral they 

 are only 7-15 p long ; 

 the contents are almost 

 homogeneous with 

 brownish black colour ; 

 the nuclei are roundish 

 and he close to the muscle 

 layer. The supporting 

 cells are very slender, with their tops only slightly expanded ; the 

 nuclei are fusiform or filiform and lie always in the expanded 

 portion. In the two points above mentioned, where the clitellum 

 shows a break, the hypodermis consists only of ordinary cells like 

 those of the extra -clitellar part and contain no glands (fig. 28). 



go- 



Im— ■-— 





}^^r- 



-b.v 



n.pt 



Fig. 2. 



Cross sections through the clitellum of tin immature 

 (A) and a mature (B) specimen. x700. c— cuticle, hy — 

 hypodermal cell, n. hp — nucleus of hypodermal cell, 

 be — basal cell, gc — clittellar gland cell, n.gc — nucleus of 

 basal or gland cell, cm — circular muscle layer, 1m — longi- 

 tudinal muscle layer, pt — peritoneum, n. pt — nucleus of 

 peritoneal cell, bv — integumentary blood vessel, cv — 

 clitellar blood vessel. 



