332 



GENERAL ORNITHOLOGY 



as I have observed before, it is like any other amoeba ; the first step 

 of development is probably a retrograde one ; for if there ensues, 

 when the spermatozoa melt into the ovum, the result affirmed for 

 mammalian ova, the original germinal vesicle and germinal spot 

 disappear, and the whole content of the ovum proper is simply a 

 homogeneous mass of granular protoplasm. In this retrograde step, 

 the organism, at the lowest possible round of the ladder of evolu- 

 tion, is called a monerula. The germinal vesicle and spot, however, 

 are speedily reconstructed, and the ovum looks precisely as it did 

 before. But observe that the actual difference is enormous ; for it 



Fig. 111. — Segmentation of the vitellus by discoidal cleavage, diagrammatic, X about 10 times, 

 after Haeckel. Only the " tread," cicatricle, or germ-yelk (Figs. 109, 6, 110, A) is represented, 

 as no other part of the whole yelk-ball undergoes the process. j4, separation into 2 ; B, into 4 ; 

 C, into 16, by 8 radial and 1 concentric furrow ; D, into many parts, by 16 radial and about 4 

 concentric furrows ; E, 64 radial and about 6 concentric furrows ; F, the whole tread broken up 

 into a mulberry-mass (morula) of cells. 



now consists of the blended substance of the original ovum and of 

 the spermatozoa ; and in this duplex or bisexed state, before any 

 further step is taken, the creature is called a cytula, — the parent 

 cell of the entire future organism. In the former state it could 

 reproduce nothing, not even itself ; for it is the strange physiological 

 law of a Dynamammba that it cannot reproduce like an ordinary 

 cell, but must evolve an entire organism, like both of those two whose 

 vital forces it concentrates, summarises, and embodies, — or nothing. 

 The first change in the parent-cell is that by which it becomes 

 broken up into a mass of cells, each of which is just like itself. 

 This process is called segmentation of the vitellus ; each one of the 

 numerous resulting cells is called a cleavage-cell. The nucleus of 



