22 INTRODUCTION. 



tions between the lymph-sacs that exist on both the 

 dorsal and ventral surfaces immediately beneath the 

 integument. 



The lymph, fed by the moisture absorbed through 

 the skin, is pumped into the veins by two pairs of 

 lymph-hearts, contractile muscular sacs, the anterior 

 of which are situated in the muscular tissue close to 

 the transverse processes of the third vertebra, the 

 posterior on the sides of the urostyle near its extre- 

 mity ; their pulsations may be observed on the back 

 of the living frog. 



The number aud extent of the lymph-sacs varies in 

 the different genera. In Rana and Pelodytes there 

 are 22, 4 unpaired and 9 pairs. The dorsal sac 

 extends from the tip of the snout to above the vent, 

 and is limited by the line of attachment which corre- 

 sponds to the canthus rostralis, the supra-orbital 

 border, the supra-temporal fold, and the glandular 

 dorso-lateral fold. The lateral sac is limited below by 

 a band on each side of the belly, which may be marked 

 externally by a slight groove ; the abdominal surface of 

 the head and body is divided into three sacs, gular, 

 pectoral, and abdominal, with partitions across the 

 praacoracoid and coracoid regions. The further sacs 

 (brachial, subbrachial, femoral, supra-femoral, inter- 

 femoral, crural, supra- and sub-plantar) belong to the 

 limbs. In Hyla there is besides a close areolar attach- 

 ment of the abdominal integument. The Discoglos- 

 sidse differ in the absence of coracoid attachment, 

 or if such exists, as in Discoglossus, it is widely 

 interrupted on the middle line ; there is, therefore, 

 no distinct pectoral lymph-sac. In Pelohates the skin 

 of the belly is attached in its posterior half. In 

 Bufo the ventral integument is more or less broadly 

 attached, together with the whole of the dorsal 

 integument. 



One of the most remarkable peculiarities connected 

 with the integument of Batrachians is the cutaneous 

 respiration, or the power which the surface of the 



