XXI, 2. Andrews: Removini»- avian blastodernis. 177 



türehtiing, dal.) durch die seitliche Ottuung bakl 8taiib in das Okidar 

 eindringen und dasselbe beschmutzen wird , entspricht der Er- 

 fahrung nicht, 



[Eingegangen am !). Juli 1904. J 



Removing avian blastoderras. 



By 

 E. A. Andrews. 



With one woodcut. 



It is well known tliat there are dit'iiculties in the way of re- 

 moving the blastoderm from an unincubated hen s egg or froni one 

 incubated less tlian twenty-four hours. In Lee's Vade Mecum it is 

 advised to tix and harden blastoderm and yolk together as "it is 

 extremely dit'ticult to separate" tliem. The two obstacles met with 

 the adherence of the blastoderm to the vitelline membrane on the 

 one band and to the j^olk on the other are circumvented by 

 hardening in situ by such excellent methods as that of Duval. 

 But this does not furuish surface views such as are often neces- 

 sary to give any adequate conception of the real condition of the 

 blastoderm. 



The foUowing method enables the novice to readily obtain 

 good mounts of transparent whole blastoderms from unincubated and 

 early incubated stages. In essence it consists in separating the 

 blastoderm from the vitelline membrane and of fixing it partially 

 and then separating it from the yolk while the latter is still fluid. 

 To accomplish this result picro-sulphuric is injected between the 

 blastoderm and the vitelline membrane and when the blastoderm is 

 partially fixed and is coherent it is removed from the yolk. 



A pipette such as is indicated in the accompanying sketch 

 is found useful. The upper i)art is larger to hold suflicient 



Zeitschr. f. wiss. Mikroskopie. XXI, 2. 12 



