ee IE 


1891.] Embryology. 839 
medullary groove, but after the egg has begun to elongate and the 
paired, secretory, adhesive surfaces of the under side of the head have 
appeared as rudiments, the position of the animal and vegetative poles. 
is still the same as in the undeveloped ovum. The head end of the 
egg is slightly elevated above the caudal end. This is due to the for- 
ward growth of the head, and the retention of the heavier yolk, farther 
backward under the posterior half of the medullary groove. The medul- 
ary groove thus comes to be inclined downward a few degrees from 
the head toward the tail, but the groove looks exactly toward the 
zenith, while the yolk looks downward in every egg, even the inclina- 
tion of the medullary groove with respect to the horizon ~~ the 
same for every egg of the same age. 
At this stage I neglected to note an extremely important fact,—viz., 
~ whether the cephalic and caudal poles of the same row of eggs were all 
of them lying in the same direction. The fact that no change of 
position occurs for a long time in the eggs of Engystoma would indi- 
cate that possibly we might find that the future cephalic pole of the 
egg bore a constant relation to the cephalic pole of the parent Engys- 
toma, such as is known to be the case in Batrachus tau. Such relations 
between parent and offspring exist to a marked degree, if they are not 
universal, in plants, and it is desirable to know to what extent the 
same rule holds with respect to animals. According to what has pre- 
ceded, the early development of Engystoma is peculiarly favorable for 
the purpose of testing the theory that the cephalic and caudal polari- 
ties of the parent are transmitted directly to the offspring, or that the 
future long axis of the embryo already conforms, even in the egg, to 
that of the parent. 
The next step in the development of Engystoma is somewhat simi- 
lar to that of Rana.’ As soon as the larve have the tail-fold well 
developed they turn over and lie on the side, curved upon themselves, 
within ghe egg-envelope. This is the condition of the eggs on the 
second and early part of the third day. On the third day the larve 
leave the egg, and then tend to fall upon the bottom of the pool or 
_ receptacle in which hatching occurs. Soon after this they begin to 
swim about actively, and, singularly enough, instead of swimming like 
a fish, for some reason, which it is difficult to make out, the larve 
revolve on their own long axes. This singular mode of locomotion is 
probably due to the peculiar manner in which the tail is vibrated. This 
mode of swimming lasts about a day, after which the larve begin to 
swim in the usual fish-like way. At this stage, when the larvae come 
to the surface, the head is in contact with the surface of the water, and — 
Am. Nat.—September.—s. n fa 



