IMARSILIA VESTITA. I99 



THE ]<:mbrvo. 



The enibiyo was very carefully studied b\' Ilanstein,* 

 and as his account is in all important particulars correct, 

 1 shall simplv give here a brief sketch of the earlier 

 divisions, as only a few minor differences were noted be- 

 tween M. z'cstita and JM. salvatn'.w which was the species 

 mainly studied by Ilanstein. 



The first division of the fertilized eg"*^' takes place 

 probablv within two or three hours after the entrance of 

 the spermatozoid. but 1 ha\'e no exact data on this point. 

 Hanstein says that in the case of j\[. salralrix about 

 twelve hours elapse before the tirst di\'ision. but in ]\I. 

 vc'itita the time is certainly much shorter. The tirst wall 

 is a vertical one and di^■ides the embrvo into two equal 

 cells. This is followed quicklv bv a nearlv horizontal 

 one in each cell, at ri^'ht angles to the tirst, and this 

 second division divides the embrvo into primar\- organs. 

 The first or basal wall, divides the embr^'o into the •• epi- 

 basal '" or forward, and the " hypobasal "' or posterior 

 parts, and the second walls dixide the epibasal portion 

 into cotyledon and stem, and the hypobasal into root and 

 foot. 



The third set of walls "octant walls,"" are not quite 

 the same in the two walls of the embryo, in the epibasal 

 quadrants the octant wall is at right angles to the others, 

 and the resulting cells consequently equal, but in the 

 hypobasal quadrants this is not the case, but the octant 

 walls make an angle of ab(nit 120*^ with the basal wall, 

 so that the octants are of \-ery unequal size. 



The eight cells of which the embryo is now composed, 

 while somewhat unequal in size, are approximately of 

 the same form, /. c. tetrahedral, and one of the cells from 



*1. c. p. 28. (2) 



