4490 Insects. 



abdomen, and which is thence derived from the abdomen of the first 

 parent. 



When these germs have reached the size of *lot\\ of an inch in 

 diameter, there appears on each, near one end, a yellowish vitellus- 

 looking mass or spot, which is composed of large yellowish cells, 

 which in size and general aspect are different from those constituting 

 the germ proper. This yellow mass increases pari passu with the 

 germ, and at last lies like a cloud over and concealing one of its 

 poles. I would also insist on the point that it does not extend itself 

 gradually over the whole germ-mass, and is therefore quite unlike 

 a true germinative vesicle or a proligerous disk. When the egg-like 

 germs have attained the size of T | th of an inch, there distinctly ap- 

 pears the sketching or marking out of the future animal. This 

 sketching consists at first of delicately marked retreatings of the cells 

 here and there, but which soon become more prominent from furrows, 

 and at last the whole form of the embryo stands boldly out. As the 

 whole idea and form of the insect is thus moulded out of a mass of 

 cells, it is evident that the separate parts which then appear, such as 

 the arches of the segments, the extremities and the oval apparatus, 

 consist at first only of rows of simple cells. This point is here beau- 

 tifully prominent, and nowhere have I observed finer illustrations of 

 the cell-constitution of developing forms. The development thus 

 proceeding, each part of the dermo-skeleton becomes more and more 

 distinct, and the increase of size of the whole is attained by the con- 

 stant development of new cells. During this time the yellow vitellus- 

 looking mass, situated at one of the poles of the embryo, has not 

 changed its place ; it has increased somewhat in size, but otherwise 

 appears the same. When the development has proceeded somewhat 

 further, and the embryo is pretty well formed, the arches of the seg- 

 ments, which have hitherto remained gapingly open, appear to close 

 together on the back, thereby enclosing this vitellus-looking mass 

 within the abdominal cavity. 



It is this same vitelloid mass thus enclosed that furnishes the nutri- 

 tive material for the development of new germs, which would be those 

 of the fourth brood or D : this development of germs here commences 

 with the closing up of the abdominal cavity, and the same processes 

 which we have just described are again repeated. 



The details of the development subsequent to this point are like 

 those of the development of ordinary insects, or of the Articulata in 

 general; and although this ovoid germ has at no time the structural 



