Insects. 4493 



continued undisturbed, through seven to nine broods, we cannot won- 

 der at the countless numbers which appear from so few original 

 individuals. 



Such are the details of the embryological development of the 

 so-called viviparous Aphides, as far as I have enjoyed opportunities 

 for their study. We will now refer for a moment to the special points 

 which have here been made out. In the first place it is evident that 

 the germs whicli develope these forms are not true eggs. They have 

 none of the structural characteristics of eggs, such as a vitellus, 

 a germinative vesicle and dot ; on the other hand, they are at first 

 simple collections, in oval masses, of nucleated cells. 



Then again, they receive no special fecundating power from the 

 male, as is the necessary preliminary condition of all true eggs ; and, 

 furthermore, the appearance of the new individual is not preceded by 

 the phenomena of segmentation, as also is the case with all true eggs. 

 Therefore their primitive formation, their development, and the pre- 

 paratory changes they undergo for the evolution of the new individual, 

 are all different from those of real ova. Another point is, these vivipa- 

 rous individuals have no proper ovaries and oviducts. Distinct 

 organs of this kind I have never been able to make out. The germs 

 are situated in moniliform rows, like the successive joints of confer- 

 void plants, and are not enclosed in a special tube. These rows of 

 germs commence each by a single germ-mass which sprouts from the 

 inner surface of the animal, and which increases in length and in the 

 number of its component parts from the successive formation of new 

 germs by a constriction-process as already mentioned. Moreover, 

 these rows of germs, which, at one period, closely resemble in general 

 form the ovaries of some true insects, are not continuous with any 

 uterine or other female organ, and therefore do not at all communi- 

 cate directly with the external world. On the other hand, they are 

 simply attached to the inner surface of the animal, and their compo- 

 nent germs are detached into the abdominal cavity as fast as they are 

 developed, and then escape outwards through a porus genitalis, 

 exactly as is the case with the eggs of fishes. Here, then, comes the 

 important question, What interpretation shall we put upon these 

 reproductive parts — these moniliform rows of germs ? 



Ignoring all existing special theories relating to reproduction, the 

 observing physiologist would be left no alternative but to regard them 

 as buds, true gemmae, which sprout from the inner surface of the 

 Aphis, exactly like the buds from the external skin of a Polype. 



Before proceeding to a discussion of the relations of this important 

 xii. 2 y 



