Wall of the Body-cavity of Vertebrate*. 



248 



with a little carmine into the body-cavity of specimens of Squatina 

 angelus (Bhina squatina, L.). Two days later the animals were 

 killed. Phagocytes laden with the colouring matter were found 

 in the nephrostomial funnels and in spaces in the kidney into which 

 these funnels led. Whether these spaces were continuous with 

 the lumen of the renal tubules could not be determined. But 

 in addition to this means of clearing the foreign matter away from 

 the peritoneal cavity, another method, as I take it, appears to 

 have been resorted to. I have satisfied myself that in the normal 

 JR. squatina there are no abdominal pores, but there are cloacal 

 pits with exceedingly thin walls towards the body-cavity. From 

 Schneider's description, I conclude that these walls were broken 

 through in his more or less pathological specimens, forming ruptures 

 on each side of the cloacal slit. They appeared as black pits pig- 

 mented with Indian-ink-laden leucocytes, wandering, as he explains, 

 into the tissue round the pore. The pigmented leucocytes were found 

 only in these two places, and the pores had opened, no doubt, I 

 consider, in consequence of pressure from within, for the spaces in 

 the kidneys are described as being choked with phagocytes. What 

 appears to have happened is, that the nephrostomes having been 

 stopped up with an accumulation of phagocytes, the pores broke 

 open, and the remaining phagocytes were there expelled, some of 

 them, however, passing into the exposed connective tissue round the 

 edge of the rupture. Another previous experiment by Schneider 

 gives further evidence on the subject.* He made a copious injection 

 of carmine suspended in sterilised salt solution into the body-cavity 

 of Salmo fario. His specimens may have been immature ; in any 

 case, unlike some of Weber's, they had no abdominal pores. But 

 potentially, I am inclined to think, they w r ere present, as the phago- 

 cytes which had engulphed the injected pigment collected at the 

 posterior end of the body-cavity, where the abdominal wall on each 

 side of the anus is very thin. Some of the phagocytes wandered 

 into this thin wall, and in one case they passed right through it and 

 formed a mass of pus on the external surface. This gives, I take it, 

 a very plain hint of what would have happened if the abdominal 

 pore had been present. There would have been no obstacle to the 

 excretion from the peritoneal cavity of the foreign matter and 

 products of inflammation. 



The abdominal pores are then excretory ducts, and (should occa- 

 sion arise) would, as Giinther suggested, aid in removing stray ova 

 and semen from the body-cavity as a part of their work, but by no 

 means as the whole of it. And if this view is correct, the body 

 cavity of fishes and of the lower Amphibia is to a great extent 

 an excretory organ, as it certainly is in the early stages of the 

 * ' Mem. Ac. Imp. Sci.,' St, Petersbourg, [8], 1895, vol. 2, JSTo. 2. 



