412 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 1925 



There is nothing visible or otherwise discernible yet discovered 

 within the <j^rowiTif( orf^anism to show what endows its cells M'ith this 

 wonderful power of arranf!;ing themselves into a new animal, which 

 is at the same time almost a replica of the parent form ; but there is 



End 



-LMe30 



Fig. 27. — Cross section through dorsal part of abdomen of 

 embryo of male honeybee. (Figure from Petrunkevitch) 

 Dph, dorsal dianhragm ; Ect, ectoderm ; EMeso, external 



mesoderm layer; End, stomach (endoderm) ; GCls, germ 



cells ; Ht, heart ; IMeso, inner mesoderm layer applied to 



stomacli wall ; Rep. reproductive organ. 



also no good reason for supposing that our ignorance of the secrets 

 of development and heredity is diiferent from any other special case 

 of ignorance that has been dispelled by research. There is un- 



_JP X.J'. 



Fit). 2S. — Various forms of young insects 

 A. a young grasshopper. B, a young roach a few minutes after liatchin?;. (", tlie 

 young of a moth ( a caterpillar). 1), a young wasp. E, a young lly (a maggot). 



doubtedly a cause for the vital processes that transform the egg into 

 the mature embiTO, and this cause will l)e un(lerstandal)le when it 

 is discovered, though, as with all other things in nature, it will be 

 understandable only in terms of incomprehensible forces. 



