insects. 4489 



places, were of mature size, and I found in them the developing 

 germs of the second brood quite far advanced. On this account it 

 was the embryology of the third series or brood alone that 1 was able 

 to trace in these observations. 



A few days after the appearance of these insects, the individuals of 

 the second brood, (B) still within their parents (A), had reached two-thirds 

 of their mature size. At this time the arches of the segments of the em- 

 bryo had begun to close on the back, and the various external appen- 

 dages of the insect to appear prominently ; the alimentary canal had 

 been more or less completely formed, although distinct abdominal or- 

 gans of any kind belonging to the digestive system were not very pro- 

 minent. At this period, and while the individuals of generation B are 

 not only in the abdomen of their parent (A), but are also enclosed 5 each, 

 in its primitive egg-like capsule, — at this time, I repeat, appear the 

 first traces of the germs of the third brood (C). 



These first traces consist of small egg-like bodies, arranged two, 

 three or four in a row, and attached in the abdomen at the 

 locality where the ovaries are situated in the oviparous forms of these 

 animals. 



These egg-like bodies consisted either of single nucleated cells, 

 of so^oth of an inch in diameter, or a small number of such cells en- 

 closed in a simple sac. These are the germs of the third generation : 

 they increase with the development of the embryo in which they have 

 been formed; and this increase of size takes place, not by a segmen- 

 tation of the primitive cells, but by the endogenous formation of new 

 cells. After this increase has gone on for a certain time, these 

 egg-like bodies appear like little oval bags of cells ; all these compo- 

 nent cells being of the same size and shape, there being no cell which 

 is larger and more prominent than the rest, and which could be com- 

 parable to a germinative vesicle. While these germs are thus consti- 

 tuted, the formation of new ones is continually taking place. This 

 occurs by a kind of constriction-process of the first germs, one 

 of their ends being pinched off, as it were, and in this way what was 

 a single sac is changed into two which are attached in a moniliform 

 manner. The new germ thus formed may consist of even a single 

 cell only, as I have often seen, but it (the germ) soon attains a more 

 uniform size by the endogenous formation of new cells within the sac 

 by which it is enclosed. In this way the germs are multiplied 

 to a considerable number, the nutritive material for their growth being 

 apparently a fatty liquid with which they are bathed, contained in the 



