704 



APPENDIX. 



that at every time an egg is laid, the egg tube is ruptured. 

 This was also observed in the sheep tick (Melophagus} by 

 Lenckart, and in certain flies (Limnobia, Psychoda, and My- 

 cetobia) by Ganin himself. 



The earliest stage observed after the egg is laid, is that in 

 which the egg contains a single cell with a nucleus and nucle- 

 olus. Out of this cell (Fig. 652 A, a) arise two other cells. 

 The central cell (a) gives origin to the embryo. The two 



outer ones multiply by subdivision 

 and form an embryonal membrane, 

 or "amnion," which is a provisional 

 envelope and does not assist in 

 building up the body of the germ, 

 which however is accomplished by 

 the cells resulting from the subdivi- 

 sion of the central single cell. Fig. 

 652 B, g, shows the germ just form- 

 ing out of the nucleus (a) ; and 6, 

 the peripheral cells of the blasto- 

 derm skin, or "amnion." Fig. C 

 shows the yolk transformed into the 

 embryo (g) with the outer layer of 

 blastodermic cells (b). The body 

 of the germ is bent upon itself. 

 Fig. 652 D shows the embryo much 

 further advanced with the two pairs 

 of lobes (md, rudimentary mandi- 

 bles, d, rudimentary pad-like or- 

 gans, seen in a more advanced stage 

 in E) and the bilobate tail (st). 

 Fig. 653 shows the first larval stage 

 after leaving the egg (m, mouth ; a, 

 rudimentary antennae ; md, mandibles ; d, tongue-like appen- 

 dages ; st, anal stylets ; the subject of this figure belongs to a 

 distinct species from Fig. 652 E). This strange form would 

 scarcely be thought an insect, were not its origin and further 

 development known, but rather a parasitic Copepodous Crus- 

 acean, whence he calls this the Cyclops-like stage. In this 

 condition it clings to the inside of its host by means of its 



First larva of Platygaster. 



