374 



division the secondary buds of tiie right side produce the pair of 

 embryos previously designated the ''dorsal'' (3) and ''right-lateral" 

 (4), while those of the left side from the '"ventral" (1) and "left- 

 lateral" (2). Tiie formation of the secondary buds is also anticipated 

 some little time before the actual division of the primary bud appears. 

 The cells of each jDrimary hud become concentrated toward each side 

 of the bud. and the line of division later appears between these two 

 thickenings. At about this time the vesicle shows in surface views 

 the four rudiments of the embryos as white, more or less opaque, 

 spots (Fig. 6). Each secondary bud soon begins to extend out from 



w. 







Fif;. 5. Photoj(ia])h of a inedian section of a vesicle in «-hich the two primary 

 Inids have just ai)])eared. The light- and left-liand bays of these buds are marked 

 B' and B" respectively. The two mesodermic pouches have expanded and fused to 

 form ttie single large extraembryonic body cavity {Ex.C). 



Fig. 6. Drawing of the surface view of a vesicle showing the rudiments of 

 the four embryos as opaque spots, which are marked by the numbers 1, 2. .S, 4. 



the primary Inid as a tube-lii<e process (Fig. 7) that grows down 

 along the inner side of the entodermic vesicle towards the Träger, 

 with which a placental connection is eventually established. 



The proximal part of the primary bud does not undergo division, 

 but forms a common cliannel connecting tiie two tubes that lead 

 from a pair of embi-yos to the common amniotic vesicle. An early 

 phase of this condition is beautifully bronglit out in a series of 

 sections of one vesicle in the possesion of the writer. The vesicle 



