256 PHYSIOLOGY OF THE INVERTEBRATA. 



The Annelida. 



(i) The Hirudinca. — The author* has examined the 

 nephriclia of Hirndo mcdicinalis. These nephridia are in 

 pairs, extending from the second to the eighteenth segments 

 (somites). Each nephridiumf consists of a much-convoluted 

 cellular tube. The cells of the tube are perforated by small 

 ducts. The nephridia (segmental organs) open externally on 

 the ventral side of the body. 



In Lnmbricus the nephridium communicates internally by 

 a wide funnel-shaped aperture (which is ciliated) with the 

 perivisceral cavity, but in Hirudo it opens internally 

 by a "cauliflower-headed" portion (the analogue of the 

 funnel-shaped aperture in Lnmlricus) into the perinephros- 

 tomial sinus. Each nephridium consists of five principal 

 parts — («) posterior lobe, (h) anterior lobe, (c) apical lobe, 

 (d) the testis lobe, (c) the vesicle, with its duct, which opens 

 externally. 



The nephridia of Hirudo are covered with a pigmented 

 connective tissue. These pigments are no doubt the 

 histohsematins of Dr. C. A. MacMunn, for he says : " I have 

 found that throughout the whole animal kingdom in each 

 tissue and organ there are present colouring matters." j 



In examining the physiology of the nephridia or segmental 

 organs of the Hirudmca, the. author obtained the excretions 

 from a large number of freshly killed leeches. These excre- 

 tions were examined by the same chemical and microscopical 

 methods used in the examination of the segmental organs of 

 the Oligocliaia and the renal organs of the Astcridca. 



The nephridia of Hirudo contain uric acid and sodium ; 

 and it may be that the uric acid is in combination with sodium 

 as sodium urate. 



* Froceedi»gs of lioyal Society of Edinhuryli, vol. 14, p. 346. 

 j- From yecppds, a kidney. 



X Proc. Birmiiujham Fliilosophical Society, vol. 5, p. 211 ; Free. Boy. Sac, 

 1886; and FhilosojiJi. Trans., 1886. 



