146 APPENDIX. [No. II. 



13. "When the ova were placed in a solution of prussiate of potash, no 

 coagulation or other change ensued. 



14. When the envelope was placed in a strong solution of corrosive 

 sublimate in alcohol, no change took place. 



15. Solutions of muriate of ammonia and common salt produced no 

 change. 



16. The solution of the envelope in nitric acid was treated with 

 ammonia when it was not again re-precipitated. 



17. The solution was then treated with potash, when the result was 

 the same as before. 



18. A solution of tannic acid gave a white precipitate with the acid 

 solution. 



19. A solution of gallic acid failed to give a precipitate with the 

 solution. 



20. When the acid solution was neutralized and treated with ferro- 

 cyanates of potassa, no change ensued. 



21. The acid solution was found to give no precipitate with acetate 

 of lead. 



22. The gelatinous, or rather the mucous envelope, was found to be 

 neutral, neither changing the colour of litmus-paper to red, nor restoring 

 reddened litmus-paper, and it was also found to have no action on 

 turmeric paper. 



From these experiments it is decidedly proved that this covering is 

 neither albuminous nor gelatinous : for had it been the former, many of 

 the above tests would have coagulated it ; and had it been the latter, water 

 would have dissolved, and tincture of galls had a sensible effect on it, &c. 

 The nearest animal product then, which it approaches in its general 

 characters, is mucus, which is known to differ in different situations of 

 its secretion. 



This mucous envelope is found to be a product exclusively of the 

 oviduct, for the ova at no period of their existence in any way possess it, 

 the proof of which is obtained from killing a frog just before spawning is 

 expected, when the ova in the ovaries will be found to have no covering, 

 and when placed in water do not swell out. Those ova, however, which 

 have found their way into the oviduct possess the mucous covering, and 

 when placed in water do swell out. The oviducts do not form the mucus 

 suddenly when the ova are about to be discharged, but keep forming it for 

 a considerable period, as I have found the oviducts to be distended with it 

 six months at least previous to the period of spawning, and even immediately 

 after the ova have been discharged are not entirely free from it, though 

 they are much contracted in size. That the substance contained in the 

 oviducts and the envelope of the ova after their discharge is identical, 

 is proved by the following experiments : 



1. When a portion of the oviduct was placed in water, it swelled as 

 the envelope when first excreted ; and if a frog before spawning be killed 

 and cut open, and then placed in water, the contents of the oviducts will 

 swell to an almost incredible size. 



2. When the contents of the oviducts were placed in acid, they 

 dissolved, and did not coagulate. 



