282 



GENERAL EMBRYOLOGY 



respectively. And from these, normal larvae developed; the 

 eight macromeres developed as the normal four would have 

 done, although under normal conditions four of the eight cells 

 and nuclei would have formed the first quartet, giving rise to 

 the apical nerve cells and anterior band of ciliated cells. 



Furthermore, the experiment of bringing about the coales- 

 cence of parts of two eggs, or even of two complete eggs, has 



FIG. 133. Four normal but diminutive plutei from the isolated blastomeres 

 of the four-cell stage of the sea-urchin, Strongylocentrotus. After Boveri. A, B. 

 in oral view. C, D, lateral view. 



been accomplished with Ascaris (Sala, Zur Strassen) and with 

 the sea-urchin (Driesch). The result is again the development 

 of a normal larva, of very large size when two entire eggs are 

 fused (Fig. 136). Even when two blastulas coalesce the final 

 result may be a single larva, though with some doubling of 

 parts. One especially interesting point is that normal develop- 

 ment may result even though the parts of the two blastulas 



