476 



HISTOLOGY 



Technic. The technic used in preparing the female reproductive 

 cells for study differs very markedly from that of the preceding part. 

 This is owing solely to the great mass of yolk which most ova contain, 

 as well as to the membranes of several kinds with which they are usually 



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b'^gftbo 



FIG. 448. Artemia salina. Several stages in the maturation of the kind of parthenogenetic 

 egg which gives off but one polar body. A, first polar spindle with 84 tetrad chromosomes; 

 B, C, formation of first polar body; D, egg nucleus, formed from the remaining dyad chro- 

 mosomes (84); E, F, G, formation of first cleavage figure. (From WILSON after A. BRAUER.) 



covered. For this reason, Flemming's fluid is rarely used, and if a general 

 fixative were demanded, we should first mention sublimate-acetic (a sat- 

 urated, watery solution of corrosive sublimate containing five per cent 

 of glacial acetic acid). Even this has to be put aside in many cases 

 where the yolk becomes too brittle, and its place is taken in most cases by 

 a mixture of picric acid and acetic acid in several combinations. In 

 some few cases the yolk can be softened or even dissolved. For instance, 

 by fixing teleost fish eggs in corrosive sublimate only long enough to 

 kill the embryo, and then completing the process in five per cent formalin, 



