632 J. T. PATTERSON 



In the earthworm, Kleinenberg ('79) has described a gemelli- 

 parous development occurring in the gastrula stage and initiated 

 by a sort of fission or budding. In the Cyclostomatous Bryzsoa 

 (Harmer '93, Robertson '03) a. primary embryo, prior to the for- 

 mation of germ layers, buds off a large number of secondary em- 

 bryos which differentiate into larvae. In the parasitic Hymen- 

 optera (Marchal '04, and Silvestri '06) the differentiation of the 

 embryos occurs relatively still earlier and consists in the disso- 

 ciation of the egg into embryonic masses, which vary in number 

 according to the species, and which later form larvae. In the 

 light of artificial blastotomy it is possible, theoretically, to have 

 the process of dissociation carried still further forward into the 

 cleavage stages even to the two-celled stage; but so far as the 

 writer knows, the ocurrence of blastotomy as early as the two- 

 or four-celled stage has never been observed as a natural phenom- 

 enon in development. 



From among the several forms having polyembryonic develop- 

 ment, one can select a series in which embryonic fission or budding 

 is carried farther and farther toward the adult stage, and as 

 Marchal has observed, one can pass insensibly from these cases of 

 budding in the egg to the more frequent and well-known phenome- 

 non in which the budding occurs after the individual has already 

 come from the egg, as, for example, in the coelenterates, Ortho- 

 nee tida, Dicyemida, platyhelminthes and tunicates. We may ask 

 then, below what point in the developmental cycle must one 

 cease to speak of asexual reproduction as budding, and refer to 

 it as polyembryony? Evidently a sharp line cannot be drawn 

 between the two. 



It is best to regard polyembryony as a precocious type of bud- 

 ding; and this, perhaps, only in the sense that it occurs early in 

 the embryonic life, and without the implication that it has push- 

 ed forward in the life cycle or superseded a budding which in the 

 ancestral froms occurred at a late period of development. This 

 would seem to be the case at least in the Polyzoa, in which the 

 embryonic budding is followed in the sessile larval stage by the 

 typical budding to produce the colony. 



