2l8 F.D.MUND 15. WILSON. 



the buds were set free from the stock, as still occurs in many 

 polyps. Here,- however, their individuality has become com- 

 pletely merged in that of the organism as a whole, which de- 

 velops, as it behaves in the adult condition, essentially as a unit, 

 the bud-formation in the merogonic development being subject to 

 a process of regulation in a manner precisely analogous to the for- 

 mation of organs in the development of a dwarf pluteus or pilidium 

 from an egg fragment. This conclusion, which is also reached 

 from the facts of regeneration described beyond, is not without a 

 broader interest in its bearing on the possible derivation of meta- 

 meric animals from linear colonies, or even on the relation of 

 Metazoa to colonial Protozoa. 



(I)} DEVELOPMENT OF FRAGMENTS OF PLANULAS. 



I made a few experiments by cutting to pieces the spherical 

 planulas of two to four hours (consisting of 128 cells or more) 

 which are placed on record as suggesting the interest of more 

 extended studies of the same kind. Like fragments of the un- 

 segmented eggs, the planula fragments quickly round out and 

 continue their development for a time apparently unimpaired, 

 and in this way were obtained from a single egg several swim- 

 ming planulas in one case nine from a single egg, in one case 

 six, in two cases five, and two or three from the remainder. 

 Though only seven planulas were thus operated the results 

 seem to show that at' this period the power of regulation is al- 

 ready somewhat diminished. Of the thirty-one fragments ob- 

 tained only two developed into normal dwarf colonies. All the 

 others produced abnormal or defective larvae, the most abnormal 

 ones, as was to be expected, arising from the smaller fragments. 

 Some failed to form stomodaeum or septa, others produced stomo- 

 daeum and the normal number of mesenteries, but no peduncle, 

 several were nearly normally formed but produced no buds, and 

 only a single pair of mesenterial filaments, one produced only a 

 single large median bud, while several of the smaller larvae showed 

 less than the normal number of mesenteries. Of the nine frag- 

 ments of a single planula six ultimately died, but the remaining 

 three pieces, including the two largest, developed into larvae all 

 of which possessed stomodaeum and mesenteries. The smallest 



