240 LITE. [Vou. XII. 
develop further. Morgan himself says (p. 117): ‘The smallest 
pluteus which I have found measured 7 X 8, and the normal 
form in the same dish 12 X 15. Another larva at the begin- 
ning of the pluteus stage measured 6 X 7. The larvae have 
apparently one-eighth the volume of the normal, and correspond 
in size very nearly to the pluteus figured by Loeb. If, how- 
ever, we compare these small larvae with the larvae derived 
from isolated blastomeres, the conclusion is forced upon one 
that these plutei have in all probability come from fragments 
of the egg having only about one-half to one-fourth of the volume 
of the egg.’ Inasmuch as the test proposed for the limits of 
divisibility rests upon the capacity for complete development 
to an embryo, or larva properly so-called, it is only these last 
figures of Morgan’s that demand consideration. It would 
seem from these that Loeb (/oc. czt.) has made his figure, one- 
eighth, too low, not having taken in account the fact, emphasized 
by Morgan, that the growth of the small blastulae, gastrulae 
and plutei is less rapid than that of the normal. 
Zoja’s results on the separation of the blastomeres of the 
ova of certain medusae must also be considered. In the sum- 
mary, p. 32, we find the following remarks: “ Medusae; Die 
Entwicklung der getrennten Blastomeren (§ und } Ei von 
Liriope mucronata, Geryonia proboscidalis, und Mitrocoma 
annae; 4, 1, 4, =4, Ei von Clytia flavidula und Laodice cruci- 
2 OE) 7B) 62 
ata) ist ganz genau in allen ihren Phasen wie diejenige des 
ganzen Eies.” — “Es bildet sich endlich immer eine schwim- 
mende Larva, aus zwei Gewebe bestehend, die von jener, 
welche aus + Ei hervorgeht, nicht unterscheidbar ist, ausser in 
den Dimensionen.” 
From this it appears that a 54 blastomere of Clytia and 
Laodice is able to develop into a swimming larva. But from 
the next statement I judge that the development cannot go 
farther; this is: “ Bei Clytia zeigten } und } Ei auch die voll- 
standig entwickelte idroide Form, und bei Liriope gab } eine 
kleine runde Medusa, in welcher die vier primaren Tentaculi 
normalerweise im Kreuz angeordnet waren.” Thus a fourth 
blastomere is the smallest portion capable of complete develop- 
ment. 
