216 



INTERNAL FACTORS 



IV. i 



without giving rise to larvae. A | macromere, on the other hand, 

 or a ^ or later blastomere, will not segment at all. 



By lowering the temperature the cleavage may be made to 

 resemble that of whole ova. 



FIG. 123. Ih/anassa : cleavage of smaller \ blastomere (AB). a, Un- 

 divided ; fc, -| embryo, from side ; c, embryo, from above ; rf, -fy embryo, 

 from above : the dot indicates the former centre of the egg ; e, J j embryo, 

 from side ; /, growth of ectoderm over the macrouiei'es ; g, formation of 

 the micromeres of the fouith generation, from below; h, ciliated partial 

 embryo of 46 hours. (After Crampton.) 



The yolk-lobe influences the character of segmentation, for if 

 it be removed CD divides like AB. More important than this is 



