170 TORREY 



fifth quartet, in turn, dexiotropically. The posterior member of 

 the fourth quartet (4^) produces the coelomesoblast, but the 

 other members of this quartet as well as the fifth quartet and 

 the macromeres give rise only to entoblast. 



I. To 6^ Cells. 



I will pass over the maturation and fertilization of the egg with 

 little comment, as Conn has described these phenomena in the living 

 Qgg and Griffin with great detail in sections. When the eggs are first 

 discharged from the segmental organs they are pressed out of shape 

 and, only after the entrance of the sperm, become spherical. The 

 small size of the eggs (about 70-80, a in diameter) adds considerable 

 difficulty to their study. During and alter fertilization what at first 

 sight appear to be spinning activities take place at the surface of the 

 egg. Soon after the entrance of the sperm the egg membrane 

 (chorion) begins to draw away from the egg itself and soon is com- 

 pletely detached. If the space that thus results between the mem- 

 brane and the egg is now examined with a high power, fine proto- 

 plasmic strands may be seen running from the one to the other. 

 These threads may vary from time to time in thickness and constitu- 

 tion and often contain granules. They remind one forcibly of the 

 pseudopodia of Groi7iia. I have found them persisting during the 

 early cleavage stages. The polar bodies lie suspended in the space 

 between the egg and the membrane and are held at one place by 

 these protoplasmic threads as guy -ropes. I would explain the for- 

 mation of these threads by the fact that, when the membrane sepa- 

 rates from the egg, the protoplasm sticks to the corrugations on the 

 inner side of the membrane and, because of its viscid nature, is 

 drawn out into threads. Similar phenomena have been described in 

 the egg of Petromyzoii (Calberla, '78). Conn recognized certain 

 striations in the space between the membrane and the egg, but did 

 not suggest their protoplasmic nature. 



As has been described in many other forms, the first cleavage 

 begins at the upper pole and cuts in somewhat more rapidly 

 here than at the lower,^ resulting typically in the formation of 

 two equal blastomeres (Text-Fig. i, A). Their nuclei imme- 

 diately move slightly toward the left in preparation for the sec- 



1 In Lepidonotus, however, where the yolk has a more uniform distribution, the 

 cleavage plane cuts at the same rate all the way around the egg (Mead, '97). 



