BY DR. KLEIN. 165 



blastoderm of the chick, it is necessar}' to intercept the eggs 

 in their passage through the Fallopian tube ; for in eggs which 

 are already laid, these processes have been gone through. 

 The investigation of these phenomena is expensive, and de- 

 pends somewhat on chance. Hens known to be in the habit 

 of laying eggs in spring and summer must be sacrificed. 

 Eggs may be examined in which the shell is either absent or 

 consists of a very thin parchment-like structure, or is in pro- 

 cess of calcification. They are placed for a few days in a deep 

 capsule containing a one per cent, solution of bichromate of 

 potash, and are hence removed to a one-sixth per cent, chro- 

 mic acid solution for one or two days. After this time the 

 part of the yolk which has the blastoderm resting on it, is cut 

 off with a razor and laid in common alcohol, in which with due 

 precaution the vitelline membrane can be readily stripped off 

 from the blastoderm. The subsequent processes are the same 

 as with the blastoderm of the trout. 



If eggs in the different stages of their passage through the 

 Fallopian tube have been obtained, it is easy to make out in 

 prepared sections, that, during the formation of the cleavage- 

 cavity, the large coarsely granular elements (filled with the 

 coarse granules of the yolk) which compose the deeper layers 

 of the blastoderm, remain lying in large numbers upon the 

 floor of the cleavage-cavity; that these are most numerous 

 towards the area opaca, that is, where the peripheral part of 

 the blastoderm lies upon the white j'olk (yolk-rim, Keimwall) 

 and that they here become continuous with the large coarsely 

 granular elements of the deeper layers of the blastoderm. 

 These elements lying on the floor of the cavity and derived 

 from the blastoderm during the formation of the cavity, corre- 

 spond to the formative elements on the floor of the cleavage- 

 cavity of the trout's egg, and those elements which, in the 

 batrachian egg, stretch up from the floor of the cavity to the 

 under surface of the dome (see fig. 175). 



Lamellae of the Blastoderm of the Chick. The study 

 of the layers of the embryo of the chick must be commenced 

 with fresh laid eggs. The egg is held with its long axis hori- 

 zontal ; the shell is cracked at its upper pole ; the bits of shell 

 in this place are removed with a forceps, and the outer mem- 

 brane torn off the exposed part ; the shell is then broken in 

 two, and the contents are let out into a flat capsule. With 

 the aid of scissors and forceps, the egg (using the word in its 

 more restricted sense) is freed from the investing albumen, 

 which is carefully poured off. After having, by means of a 

 lens, acquired a general notion of the grosser anatomical re- 

 lations as they present themselves on a surface view (such as 

 the Area pellucida, A. opaca, Pander's " nucleus of the white 

 yolk," etc.), we pour into the capsule in which the egg lies a 



