EMBRYOLOGICAL INVESTIGATIONS 261 



are more abundant than the blastomeres, so that the 

 greater part of the embryo is formed from the 

 unfertilised kalymmocytes or follicle cells. If now 

 we imagine this carried one step further, if we sup- 

 pose the blastomeres, or fertilised elements, to be 

 completely absent, then the whole embryo would 

 be formed by an aggregation of unfertilised cells, 

 and the process would become most suggestively 

 similar to that by which a Sponge gemmule is formed. 

 The last series of phenomena to which I wish 

 to refer are those resulting from the natural 

 or artificial division of an egg, in the early 

 stages of its development, into two or more 

 fragments. In 1869, Haeckel, while studying the 

 development of Crystallodes, a genus of Siphono- 

 phora or pelagic Hydroids, was struck with the 

 fact that the polyhedral cells of which the egg 

 consisted at the close of segmentation exhibited 

 active amoeboid changes of shape, and appeared to 

 possess a certain amount of independence. The 

 idea occurred to him to test this power of inde- 

 pendent existence by breaking up the embryo into 

 fragments, and following their fate. By means of 

 needles, eggs at the close of segmentation on the 

 second day of development were broken into two, 

 three, or four pieces, and it was found that these 

 not only lived for eight or ten days, but developed 

 and gave rise, in almost normal manner, to 

 rudimentary Siphonophoran colonies. These ob- 

 servations of Haeckel's are the earliest experiments 

 on lines which have recently led to remarkable 

 results. 



