A3IBLYST0MA PUNGTATUM. ■ 13 



seen in the distal or free end of the limb, dividing it into two lobes 

 each of which becomes a digit ; the outer one, when the limb is 

 directed backward, becoming; the first or most anterior digit and 

 the inner one becoming the second. A slight flexnre or bend in 

 the limb now makes its appearance which indicates the ])osition of 

 the elbow-joint. The opening of the month makes its a|)pearance 

 usually at about this stage or later. Plate 3, Figure 19. Soon 

 after the first two digits are thus marked out, the balancers begin 

 to diminish in size, becoming more and more slender but not de- 

 creasing in length. Plate 4, Figure 21. The mouth-groove is 

 now fully indicated, but the opening appears first in the central 

 portion of the groove and extends gradually in both directions, 

 until the mouth has attained its full size. A side view shows that 

 the tail has become longer, the dorsal and ventral fin-like areas 

 have grown rapidly and the rectum is distinctly seen opening into 

 the cloaca; the position of tiie mouth too has changed, being much 

 farther forward. This condition is reached from the twenty-fourth 

 to the twenty-sixth day after the formation of the vitelline plug. 



The anterior limbs continue to grow rapidly; the second digit 

 growing faster and quickly becoming much larger than the first 

 and at the base of the second digit on tiie inner side of the fgot 

 appears a small process which is to develop into the third digit. 

 Plate 4, Figure 2-1. The balancers are still more slender, the 

 blood has nearly stopped circulating in them and they are of but 

 little use. A central artery and vein are seen in the balancers 

 when they first bud out from the side of the head, and these 

 increase in length with the growth of the balancers; so that when 

 the latter are fully developed the blood may be seen rapidly circu- 

 lating througiiout the length of these a])|)endages ; as they grow 

 more and more slender there is less and less blood sent to them, 

 until when they are in the condition represented in Figure 21, 

 Plate 4, there are only a few stray corpuscles to be seen, which 

 slowly work their way in single file to the extremity of the appen- 

 dage and passing through the capillaries, as slowly wend their 

 way back again. Circulation in the balancers now soon ceases and 

 being of no further use to the animal, these ap|)endages are no 

 longer retained. While watching through the microscope, a speci- 

 men which had but one balancer left, and that a very slender one 

 without any blood circulating it, I noticed that the creature would 

 occasionally give a number of quick, violent shakes with its liead; 

 4 



