Early Development of the Hen's Egg. 109 



certain number of ben's eggs sbow abnormal relations existing be- 

 tween the two axes, and the writer has found a similar condition 

 in the pigeon egg. In each of these species the percentage of abnor- 

 mal axes was found to be small. It seems highly improbable, there- 

 fore, that four out of five eggs taken at random, and in the two- 

 celled stage, would later show abnormal axes. The final answer to 

 the question, however, could only be obtained by studying a two- 

 celled stage and noting the plane of the furrow, and then after in- 

 cubating the egg until the axis of the embryo became visible, it 

 would be possible to determine the point in question. This would 

 necessitate a much more extensive study than the object of this paper 

 calls for. The problem, furthermore, has lost much of its earlier 

 significance, inasmuch as it has not proved to be a fundamental law 

 of development. 



In sections taken transverse to the first cleavage furrow (Fig. 2) 

 the membrane is seen to cut almost through the fine granular portion 

 of the disc, and is peculiar in that it arises from a membrane plate, 

 which, at both sides, is continuous with the perivitelline space. In 

 section the membrane does not extend down from the membrane plate 

 as a straight line, but is wavy (Fig. 3) ; and while this condition may 

 be the result of unequal contraction of the materials, caused by the 

 fixing and hardening fluids, yet it obtains for all of the earlier mem- 

 branes. 



Another point of interest brought out by the section (Fig. 2) 

 is the depression in the surface of the disc just above the cleavage 

 membrane. This is, of course, the cleavage furrow, which in this 

 egg stood out with remarkable clearness in the living condition, 

 but in most eggs it is practically wanting (Fig. 11). The lack 

 of a furrow is the cause of the indistinctness of the early cells. In 

 this respect, the early cleavages of the hen's egg differ greatly from 

 those of the pigeon's egg, for in the latter their clearness is such as 

 to permit photographing the living cells, while in the former, 

 photographs are impossible, except in a few cases. 



After the division of the first cleavage nucleus the daughter nuclei 

 migrate peripherally in a line lying at right angles to the cleavage 

 membrane, and are always elongated in the direction of motion. In 



