383 



development here commences with the closing up of the abdomi- 

 nal cavity, and then the same processes which we have just 

 described are repeated. 



The details of the development subsequent to this time, the 

 formation of the different systems of organs, &c., are precisely 

 like those of the development of true oviparous Arthropoda in 

 general ; and, although the ovoid germ has, at no time, the struc- 

 tural peculiarities of a true ovum, such as a real vitellus, germi- 

 native vesicle and 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 ova, — if this comparison of parts can be admitted, 

 then the analogy of the secondary phases of development between 

 these forms, and true ova of the Arthropoda can be traced to a 

 considerable extent. 



These secondary phases of development need not here be de- 

 tailed, for they correspond to those described by Herold, KoUiker, 

 of the true ovum in other Insecta, and which, too, I have often 

 traced in various species of the Arthropoda in general. 



When the embryo is fully formed, and ready to burst from its 

 capsule, in which it has been developed, it is about one sixteenth 

 of an inch in length, or more than eight times the size of the 

 germ, when the first traces of development in it were seen. 

 From this last mentioned fact, it is evident that, even admitting 

 that these germ-masses are true eggs, the conditions of develop- 

 ment are quite different from those of the eggs of the truly vivi- 

 parous animals, for, in these last, the egg is merely hatched in 

 the body instead of out of it, and, moreover, it is formed exactly 

 as though it was to be deposited, and its vitellus contains all the 

 nutritive material required for the development of the embryo 

 until hatched. In the Aphididae, on the other hand, the de- 

 veloping germ derives its nutritive material from the fatty liquid 

 in which it is bathed, and which fills the abdomen of the parent. 

 The conditions of development in this respect, are here, therefore 

 more like those of the Mammalia, and the whole parent animal 

 may be regarded, in one sense, as an individualized uterus filled 

 with germs ; for the digestive canal, with its appendages, seems 

 to serve only as a kind of laboratory for the conversion of the 



