14 S. F. CLARKE. 



as these were repeated I ?aw the balancer gradually break off at its 

 base or proximal end and finally becoming entirely free, fall to the 

 bottom of the dish, leaving the animal free of these embryonal 

 appendages, for which it had no farther use. Plate 4, Figure 22. 

 This observation was made upon a specimen twenty-eight days 

 after the formation of the vitelline plug. In examining twenty- 

 five specimens of this same age I found two in which both 

 balancers were still present; three in which one still remained, 

 and twenty in which both had disappeared. In all of these speci- 

 mens development had progressed to the condition indicated by the 

 presence of the rudiment of the third digit on the anterior limbs. 

 Consentaneous usually, though sometimes a little later than the 

 appearance of the third digit on the anterior limbs, appear a pair 

 of small lobes on either side of the cloaca which are to develop into 

 the posterior limbs. The progress of development in these appen- 

 dages is like that of the anterior ones. The processes elongate, a 

 slight indentation in the centre of the distal end appears, which 

 increasing in size as the lirab grows, forms two digits, the 

 first and second ; from near the base of the second, a process 

 buds out which develops into the third digit; from near the base 

 of tiie third digit buds out the fourth, and from near the base of the 

 fourtii buds out the fifth digit of the posterior limbs. The first 

 indication of the first two digits of the posterior limbs occurs at 

 about the same time that the fourth and last digit of the anterior 

 limbs appear. Plate 4, Figures 23 to 28. All the external parts 

 of the animal being now formed, the creature being about sixty 

 days old, it undergoes no external changes beyond a general 

 growth until the branchife begin to decrease in size as they are 

 being resorbed. Plate 4, Figure 29. This change takes place in 

 specimens roared in aquaria at about one hundred days from the 

 beginning of segmentation. The process of resorption of the 

 branchiae begins at their distal ends; the outer branchial-processes 

 become shorter and disappear, the outer portion of the main body 

 of the branchiiB become shorter; then the inner processes disappear 

 and nothing is left but three pairs of small rounded processes 

 which are slowly absorbed; it taking as long usually for this latter 

 part of the process to take place as it does for all tiie first portion. 

 The whole process occupies from three to five days. Thus in a few 

 days they change from water to air-breatliers, from a less to a more 

 highly specialized organization, and leaving the water take up their 

 abode in damp localities upon the land. 



