8O EDWARD DRAKE CRABB. 



'99) ; the nemertean Cercbratulus (Coe, '99) ; the prosobranch 

 Fasciolaria (Hyman, '25) ; the gastropod Limax (Mark, 'Si) and 

 in several other forms. 



The first polocyte forms a protuberance (Fig. 51) which soon 

 becomes a pedtmculated body due to the constriction of the stalk, 

 and at about this time yolk granules obliterate the clear area. 

 The first polocyte may remain attached to the ovum, but more 

 often it becomes entirely disconnected and often may have 

 migrated into the surrounding albumen a distance equal to twice 

 the diameter of the vitellus before the first cleavage occurs (Fig. 

 34). Although in this work hundreds of living eggs were ob- 

 served undergoing maturation and cleavage and these stages 

 studied in a great number of sectioned eggs, I have never found 

 a case in which the cytoplasm of either polocyte had divided to 

 form another body such as frequently occurs in molluscan and 

 other eggs, and as is figured by Kostanecki and Wierzjeski ('96) 

 in Physa fontinalis. 



Within about fifteen minutes after the first polar body becomes 

 pedunculated the animal pole is free of most of the yolk material 

 thus giving this region a clear appearance ; then the second polar 

 body appears as a clear, slightly bulging region near the same 

 point where the first was formed. It reaches its maximum pro- 

 portions in one to two minutes more, and in a total of three to 

 five minutes from the time the animal pole of the egg becomes 

 clear the second time, the second polar body is completely formed, 

 and the animal pole is again darkened by the return of the yolk 

 materials. Thus the entire cycle resulting in the extrusion of the 

 first and second polocytes is completed in about seventeen minutes. 

 This schedule holds only in water having a temperature of about 

 20-22 C. A drop in the temperature of two to five degrees be- 

 low twenty has a very noticeable retarding effect on the maturation 

 of the egg. Kofoid ('95) found that temperature has a profound 

 effect upon the eggs of Lima.v. Vignal ('n) observed that this 

 is also true of L. stagnalis eggs. Brynes ('99, p. 207, 209) found 

 that in Lima.v agrestis the first polocyte is formed and extruded in 

 two minutes and the second is formed and becomes detached in 

 the same length of time. In the living eggs of L. s. appressa the 

 chromosomes of the first polocyte may often be seen arranging 



