No. 2.] EARLY DEVELOPMENT OF AMBLYSTOMA. 349 



as a consequence of the contraction of the yolk, or are to be 

 considered with Max Schultze ('63) as an expression of a radial 

 arrangement of the yolk particles, I am unable to determine. 



The origin of the furrow with reference to the slit-like orifice 

 already described has been carefully studied. Unless special 

 attention be directed to this, one is very apt to infer that it is 

 the beginning of the first cleavage. More careful study shows 

 the two are entirely independent, and that no fixed relation 

 exists between them. In Petromyzon, Calberla ('78) believed 

 the two to coincide. 



It is by no means always the case that the first furrow divides 

 the egg into two equal parts ; it may depart so far from a 

 meridional that the segments formed are quite unequal, as 

 observed in the Frog by Prevost and Dumas ('24), Rusconi ('36), 

 Newport ('5i), and others. Neither do the ends of the furrow 

 always unite with each other in a straight line, but are often 

 joined in such a manner that an obtuse angle is formed. 



Sections of this stage show that the yolk is highly dif- 

 ferentiated, the granules at the vegetative pole being largest, 

 and gradually decreasing in size toward the animal pole until the 

 upper portion is constituted of a finely granular protoplasm, 



Secotid cleavage. — In many cases before the ends of the first 

 furrow have reached the inferior pole, the appearance of a 

 second set is foretold by the rapid closing of the groove at the 

 dark pole ; this continues until there is but a faint indication 

 of its presence. 



The second furrows begin at the first, and extend in either 

 direction at right angles to it (Fig. 6). Their progress is in all 

 essentials like that of the first, and in i hr. and 46 min. after 

 the time of appearance they have reached the opposite pole. 



Variations in the formation of the second set of furrows are 

 not uncommon. The point of origin may be at the pole or at 

 a greater or less distance from it. Newport ('51) observed this 

 eccentric origin, and believed that the second furrows formed 

 segments which on one side were always larger than those on 

 the other. 



Instead of a right angle, acute and obtuse angles may arise 

 in such a manner that they form an X, as figured by Prevost 



