135 



Pki:i.iminai;v Aii oint uv tiii: 1 )i;vi:i,(ii\ment ok Iviiiixistoma. Bv A. J!. 



ll.KKV. 



EmHKVOLO<.Y ok TIIK Cl'lTI.lKKK.K. I'.Y I ). W. MoTTIKR. 



Vakiation IX Kthk.osto.ma. By W. J. ^foKNKHArs. 



I^i.oou Coiu'USCLKs OK THE Very Youni; IIiMAN Embryo. By" I>. W. Denxi- 



EMl!RYOl,0(iY OF THE FrOO. By A. J. BiGNEY. 



Tlu' euil)ryology of the frog is an old subject, yet few of our smaller institu- 

 tions and many of the larger colleges and even some universities often do but 

 little work on the frog in this line. The material is so abundant that it seems 

 that it ought to be studied some at least even in our high schools. One difficultv 

 in the way, and perhaps the greatest, is a good method of manipulation. Manv 

 lind thi> trouble and give up almost in desjiair. 



It is the chief object of tiiis paper to present what I consider the easiest and 

 best method of manipulation. By this method even the inexperienced student or 

 the amateur may soon be able to do fairly good work. 



Eggs obtained very early in the morning may show the first process in matura- 

 tion, viz.: the formation of the polar bodies. This can be observed better in the 

 Ami)lystoma, or even more easily in the common ])oiid snail, the Di/mnacvs or 



P/l l/.Srt. 



In order to preserve liie egys for pernianent mounting or set'tioning, they 

 should l)e killed and partially hardened in alcoholic-picro-suljihuric ai'id. The 

 alcohol used in this solution should be :50 per cent. The eggs should remain in 

 this solution from six to twelve hours, dei)ending upon the age of the egg. Before 

 putting them in this solution, most of the gelatinous substance should be removed 

 by a needle or similar instrument. Next wash a few minutes in 30 per cent, alco- 

 hol, then transfer to 'lO jier I'cnt. for an hour, then to 70 per cent, for two to four 

 days. 



The 70 per cent, alcohol passes through tiie membrane covering the egg and 

 [)ushes it a short distance from the egg proper, so that it can easily be clipped with 

 a pair of sharp scissors, and the egg is readily removed. If the alcohol is much 



