AMBLYSTOMA PUNCTATUM. 15 



To recapitulale briefly. 'After segmentation there appears around 

 the lower pole of the egg an area made up of large cells, which, at 

 first hemispherical, then oval and finally circular, forms the vitel- 

 line plug of Ecker. This plug protrudes from the egg, then sinks 

 into it, while from the diminishing area around the disappearing 

 plug, stretches away the anal portions of the medullary folds with 

 the medullary groove midway between them. The two folds grow 

 forwards and unite near the opposite pole. The medullary folds 

 close in and unite forming the neural tube. The body elongates; 

 is covered with cilia and rotates horizontally upon its axis. The 

 head is marked off and the optic vesicles appear. The branchial 

 lobes and the lobes of the cephalic-balancers appear ; soon fol- 

 lowed by those of the anterior limbs. The pericardial region is 

 marked off and the pulsations of the heart are visible. The nasal 

 pits and the position of the mouth are indicated. The tail and the 

 dorsal fin grow rapidly and the branchial lobes are divided into 

 three pairs of branchiae. The branchias give off processes, the eyes 

 develop rapidly and the mouth is moving forward. The constric- 

 tion takes place across the ventral surface of the neck, and the 

 balancers now fully developed become capitate. The branchire 

 become fully developed ; the balancers become more and more 

 slender as the anterior limbs increase in length, and the blood hav- 

 ing ceased to circulate in the balancers they drop off. The anterior 

 limbs now develop with rapidity, the first and second digits being 

 formed first, then the third, and finally the fourth. The first two 

 digits on the posterior limbs are formed as the fonrth digit on the 

 anterior limbs is budding out ; then the third, fourth and fif\h 

 digits ai'e developed in succession. About the one hundredth day 

 after segmentation has besun, the branchiae are resorbed and the 

 animal enters the adult state. 



Such was the case at least in those individuals which, having 

 the most perfect branchise and the greatest amount of food, grew 

 and developed most rapidly. Other specimens, however, which 

 were surrounded by less favorable conditions develojied more 

 slowly. One which was hatched from the egg about the middle 

 of May, retained its branchise until the last week in the follow- 

 ing October, over six months, when, as the branchite were 

 being resorbed, the animal suddenly disappeared from my aqua- 

 rium during the night. From the time when the young are 

 hatched to the period of the changing from the branchiate to 



