Insects. 4491 



peculiarities of a true ovum, such as a real vitellus, a germinative 

 vesicle and germinative dot, yet, if we allow a little latitude in 

 our comparison and regard the vitellus-looking mass as the mucous, 

 and the germ- mass proper as the serous fold of the germinating 

 tissue, as in true eggs, — if, I repeat, we can admit this comparison of 

 parts, then the analogy of development between these germs and true 

 eggs of insects may be traced in considerable detail. 



This comparison I have been inclined to admit, at least in part, 

 from the striking resemblance of these developing forms at certain 

 stages,, with the embryological forms of spiders as they have been 

 figured by Herold, and as I have myself traced them. When 

 in spiders, the serous fold of the germinating tissue has extended so 

 as to cover two-thirds of the developing form, leaving the vitelline 

 mass on the dorsal surface near one of the poles, the whole embryo 

 quite resembles that of a developing Aphis just before the arches of 

 the segments close up on the back. 



With this view of the relative parts of the germ, the following would 

 be the details of the development of the different systems, and in the 

 noticing of which I shall follow Kolliker. 



1. The germinating tissue consists of two parts ; a serous and 



mucous fold. 



2. The abdominal plates arise from the serous fold, sprout out 



towards the vitelloid mass, pass over it, and unite on the dor- 

 sal surface of the future animal ; on the opposite side are 

 formed plates which do not unite, but are formed into the 

 hind legs. 



3. The wings are lateral limbs. 



4. The first traces of the abdominal column appear in the chain of 



abdominal muscles situated between the nerves and the 

 intestinal canal. 



5. The nervous system in all its parts arises from the serous 



fold, as well also as the organs of sense. 



6. The mucous fold, or the vitellus-looking mass serves no purpose 



in the formation until the closing in of the visceral plates. 



7. Thus enclosed in the abdominal cavity, it is not transformed 



directly into the intestinal canal, but simply furnishes the 

 material from which the component cells of the said canal 

 and its hepatic diverticula are formed. It also furnishes the 

 material from which the new germs are formed, as already 

 shown. 



