INTEGUMENT. 23 



skin possesses of effecting those cbanges in tbe blood 

 which are usually jjerformed by the lungs or gills, 

 and by which frogs may remain active for long 

 periods under water. Residts of various experiments 

 have proved that pulmonary respiration alone is not 

 sufficient to support life without the aid of that of the 

 cutaneous surface ; whilst some of the tailed Batra- 

 chians have lately been shown to be deprived of both 

 lungs and gills, so that the contrary does not hold 

 good for them. But in order to carry out this im- 

 portant function it is of course necessary that the 

 surface be kept in a moist state, and this is effected 

 by a secretion of fluid from the skin itself. 



An immense ,number of close-set glandular cseca 

 open upon the surface of the skin, the slime-cells, in 

 addition to which a greater or lesser number of larger 

 poison-secreting glands are scattered or disposed in 

 very conspicuous prominent aggregations, such as the 

 dorso-lateral fold of Bava, the large dorsal warts of 

 Bufo and Bomhinator, and especially the so-called 

 parotoids, situated above the ear in Bufo and Alijtes, 

 and a similar gland on the calf of Bufo calamita 

 (Fig. 9, p. 24-). These glands are pierced with large 

 pores, visible to the naked eye or with the aid of a 

 low magnifier. A round gland, the frontal or pineal 

 gland, the homologue of the so-called parietal eye of 

 reptiles, is more or less discernible under the skin 

 of the forehead in front of and between the eyes ; this 

 gland, in the early stages, was connected with the 

 brain. The presence of lime concretions in the skin 

 of old specimens of Bifo vulgaris has been first 

 pointed out by Leydig. The same have been found 

 in B. calamita by 0. Seeck. 



A character which does not appear to have been 

 noticed before is the presence of a filiform line or 

 raphe, on which the skin is much thinner, extending 

 along the middle line of the back from the snout to 

 the extremity of the coccygeal region in all specimens 

 of Bufo. This raphe, which may best be observed on 



