704 



APPENDIX. 



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

 This was also observed in the sheep tick {Melopliagus) by 

 Leuckart, and in certain flies {Lhmiobia, Psychoda, and My- 

 cetohia) 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 b, 

 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 ; at, 

 rudimentary autennai ; 7nd, 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 Cydo^ys-like stage. In this 

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



First larva of Platygaster. 



