Ryder.] 04(J [Oct. 4, 



If we now turn to the Batracliia in quest of integumentary glands 

 which bear a still greater resemblance to the sudoriferous or sweat glands 

 of Mammalia, we find them on the balls of the toes and integumentary- 

 thickenings of the footpads of certain Salientia. Integumentary glands 

 with a long duct and a short tubular secretory portion have been described 

 by F. Leydig* from the tips of the digits of Bufo, Pelobates, etc. The 

 structure of these organs, moreover, corresponds exactly to that of a very 

 immature or embryonic sweat gland which has become provided with a 

 duct or has acquired a lumen. They have ihe same lining of secretory 

 cells in the deeper glandular portion covered by longitudinal muscular 

 fibres. They have already acquired a long non-glandular eflerent duct, 

 which is evidently homologous, so far as structural details are concerned, 

 with the efferent ducts of the sweat glands of mammals. 



In the light of all the evidence now at our command, the following con- 

 clusions seem to me to be warranted : 



1. That the integumentary glands of Batracliia and the sweat glands of 

 mammals have had at least a common ancestral origin. 



2. The method by which an integumentary gland as simple as that of 

 the Batracliia might become converted into a sudoriferous gland would in- 

 volve, in the first place, a comparatively slight change of function, and, in 

 the second place, simple elongation in the direction of its own axis and 

 the differentiation of an outer non-secretory portion serving as a duct and 

 a deeper glandular portion. Some of the steps in this process have been 

 alluded to, and it only remains for us to suppose that as a result partly of 

 the great thickening of the epidermis in mammals that the eflerent ducts 

 have acquired greater length while the simple tubular glandular portion 

 has simply grown in length and become pressed into a close coil, as its 

 functional importance became greater. 



3. That the Theromora may have possessed integumentary glands, 

 seems not unlikely from the fact that they are believed by Prof. Cope to 

 be the most batrachian-like reptiles. 



4. It is equally probable that, with the change of habit from that of a 

 water and moisture-loving animal to one of terrestrial habits, the primary 

 form of integumentary gland would undergo important functional changes 

 or adaptations, as great or greater than the change in form of the gland. 



5. The principal change in the character of the integumentary glands is 

 in their form. They pass gradually from a rounded globular form in 

 lower types to a more elongate tubular and even much coiled form in the 

 higher types, while preserving essentially the same morphological struc- 

 ture. The writer therefore believes that there is no escape from the con- 

 clusion that the comparatively complex sudoriferous glands of higher 

 types have arisen by diflereutialion from the simpler defensive or poison- 

 secreting, integumentary glands of some lower type in which they closely 

 resembled those of the living Bati'achia. 



*Ueber den Ban der Zehen bei Batrachiern und die Bedeutung dcs Fersenknocheiis. 

 Morph. Jahrb., ii, 1876, pp. 165-196, PL viii-xi. 



