FROM EGG TO INSECT SNODGRASS 391 



cells. It is fortunate that the body cells do not impress their char- 

 acters on the germ cells, else the offspring would inherit all the mal- 

 formations of the parents and all the results of accidents, amputa- 

 tions, and diseases that may befall the parents. 



Enough has now been said of the germ cells, since we have traced 

 both their origin and their final development into mature reproduc- 

 tive cells. Something might be said of the intervening part of their 

 history in the reproductive organs of the parent individuals, show- 

 ing how they are here multiplied and nourished, but this would 

 take too much time from our main theme, which from here on will 

 be concerned only with the history of the body cells, or the develop- 

 ment of the young insect from tlie blastoderm. 



THE GERM BAND 



In the blastoderm stage (fig. 10 C, E), the developing insect 

 consists of a mere cellular sac {Bl) inclosing the yolk {Y) and a 



DBl DBl 



A GB B GB 



Fia. 12. — The formation of the germ band (OB) as a thickening 

 of the cells of the ventral side of the blastoderm, the cells of 

 the dorsal side, or dorsal blastoderm (DBl), remaining thin. 

 A, lengthwise section of egg. B, cross-section. 



few nuclei left behind in the latter, and is surrounded by the 

 vitelline egg membrane (D, Vit) and the chorion (fig. 2, Oho). 



The next thing that happens in development consists simply of 

 a thickening of the cells in a band along what is generally the 

 more convex side of an elongate-oval egg (fig. 12 A). This sur- 

 face is called the ventral side of the egg, because it is to be the 

 under surface of the fully formed insect. The ventral thickening 

 of the blastoderm is known as the ge7'm band {GB). It must be 

 explained here that the word " germ," unfortunately, will appear 

 in many embryological terms, but without implying that the parts 

 so named have anything to do with the germ cells. The use of the 

 word " germ " in two senses was started long ago when distinc- 

 tions were less finely drawn than now, and more exact terms have 

 not yet come into general usage. The germ band may be regarded 

 as the beginning of the embryo; its edges grade off into the thin 

 blastoderm cells still covering the rest of the egg, and known as 

 the dorsal blastoderm (fig. 12 A, B, DBl). 



