274 On the Brood-cavities of the Surinam Toad, 



to tVesli investigations of my own, I nevertheless consider 

 tliat I may abide by my formerly published interpretation ; 

 and in this I am confirmed not merely by what I have learned 

 from a multitude of subsequent investigations upon the struc- 

 ture of the cutaneous glands in other Amphibia *, but even, 

 in addition to this, by the fresh facts adduced by Klinckow- 

 strom. 



In the first place, it can hardly be denied that great agree- 

 ment prevails between the structure of the alveoli and that of 

 the dark or " poison "-glands, which extends, for instance, to 

 the pigmentation of the wall. The only real point of differ- 

 ence consists in the fact that, as I likewise pointed out at 

 the time, the alveoli are clothed with " a delicate pave- 

 ment-epithelium," as opposed to the other kind of cellular 

 coating of the cutaneous glands. But such a modification of 

 the elements of the epithelium could still without difficulty 

 be derived from the transition of the gland into the alveolate 

 cavity. With reference to my remark that the smooth 

 muscles which I found in the connective-tissue layer of the 

 environment of the alveoli " are otherwise wanting in the 

 corium," it should be borne in mind that this observation 

 dates from the year 1857. At a later period knowledge of 

 the occurrence of smooth muscles in the corium, on my part 

 also, was further advanced f. 



Of especial importance in connexion with the question 

 under discussion is the nature of the operculum. My former 

 short account says nothing as to this part of the cell, probably 

 because at that time I was unable to form a clear idea of its 

 structure — as, moreover, Mayer, as shown above, changed 

 his views with regard to it. Klinckowstroin is the first to be 

 in a position to furnish detailed information as a result of 

 careful investigation. 



The author in question points out that the operculum 

 possesses a structure altogether different from that of the 

 surrounding parts. He states that under a strong raagnifying- 

 power it represents a disk of '' corneous matter," and exhibits 

 a horizontal striation, which may even assume the appear- 

 ance of a fibrillar structure; that, from the nature of the 

 insertion of the operculum into the margin of the alveolus 

 and other physical properties, the structure gives rise to 

 the impression that it has proceeded from a substance which 

 was originally of a slimy viscid nature and subsequently 



* I gave a final resumi of my papers devoted to the cutaneous gland 

 of Amphibia in " Zum Integument niederer Wirbelthiere," ' Biologischea 

 Centralblatt/ 1892, p. 458. 



t Cf. op. at. (' IJiologisches Centralblatt,' 1892, p. 451). 



