Chap, vii.] RENAL ORGANS OF CHORD ATA. 257 



the larvae of insects, and a large quantity of renal ex- 

 cretion is collected in the rectum during the pupal 

 stage. This phenomenon may, as Gegenbaur has 

 pointed out, be well brought into relation with the fact 

 that it is at this stage that the " most intense plastic 

 activity is going on in the organism in con- 

 nection with the development of the perfect body." 

 The blowfly, when it first emerges from the pupa 

 case, excretes a semi-solid mass of nearly pure 

 uric acid (Lowne). 



Peripatus is remarkable for the possession of 

 organs which have a general resemblance to the seg- 

 mental organs or nephiidia of the earthworm and other 

 Annulata, and are like them found in all the segments 

 of the body, but those in the three foremost pairs of 

 legs are very rudimentary. A typical nephridium 

 opens at the base of each leg ; the tube leading to the 

 opening is narrow, but is continued internally into a 

 large sac, which appears to act as a bladder or collect- 

 ing organ ; this sac is continuous with a coiled tube, 

 which opens by a funnel-shaped orifice into the cavity 

 of the bodv. 



/ 



No definite information has been acquired as to the 

 possession of a renal gland by Amphioxus. The 

 Urocliordata are remarkable for the fact that the 

 uric acid secreted from their blood is not carried away 

 to the exterior, but collected into spherical vesicles 

 of large size, which lie in a mass round the intestine ; 

 in Lithonephrya the cavity of the renal organ is 

 almost filled by a single large concretion ; in other 

 Molgulidse, where the presence of uric acid has been 

 definitely proved by the colour reactions given with 

 nitric acid and with ammonia (" murexide test "), the 

 renal organ has the form of a sac, which lies close to 

 the pericardium. 



In the Vertebrata we find that, with a general 

 resemblance to the nephridia of the ringed worms, the 

 R 16 



