446 M. N. Cholodkowsky on the 



" frontal piece " (the " cephalic segment " of Hatschek) > 

 (2) of a series of limb-bearing metameres, which are homo- 

 logous with one another ; and (3) of a cerci-bearing end- 

 segment. I have already adduced evidence against the view 

 that the antennae and cerci are not homologous with the legs, 

 and I consider it superfluous that I should here revert to the 

 question. I will merely point out that although the antennae 

 are not pre-oral and belong to the primary trunk, nevertheless 

 the pre-oral segment is actually present and is separated from 

 the rest of the body by the antennary groove.' Whether this 

 pre-oral segment is comparable to the body of the Trocho- 

 sphere or not is very questionable. On the one hand, this 

 comparison is not to be rejected because the pre-oral segment 

 contains no coelomic cavities, while on the other the Insects 

 have certainly receded so far from their ancestors the Annelids 

 that a repetition of the Trochosphere stage in their develop- 

 ment may also be entirely omitted. The fact that the pre- 

 oral ganglia develop from rudiments which are separated 

 from the ventral chain is scarcely to be considered of such 

 high importance as has been ascribed to it by certain investi- 

 gators *, since, as we have already seen, each ganglion of the 

 ventral chain may also arise from a separate rudiment. That 

 the pre-oral segment contains no coelomic cavities is perhaps 

 explained by the rudimentary character of its appendages 

 (labrum), and it is at the same time also advisable to wait 

 for detailed investigations upon the development of this seg- 

 ment, in which perhaps, as in the " end-segment " of Blatta 

 germanica, rudimentary coelomic cavities will be discovered. 



As regards the embryonic envelopes, the question as to 

 their morphological value is answered in very different ways. 

 P. Mayer f regards the formation of the embryonic envelopes 

 as a summary ecdysis on the part of the embryo, a view 

 which is also adopted by Balfour. Tichomirow \ and 

 Emery § consider it possible to compare the embryonic enve- 

 lopes of Insects with the carapace of Crustacea. Kennel || 



* Schimkewitsch, "Etude sur le d6veloppemeut des AraigntSes," Arch, 

 de Biologie, t. vi., 1885, pp. 515-584, pis. xviii.-xxiii. The same in 

 Russian, St. Petersburg, 1886. 



t P. Mayer, " Ueber Ontogenie und Phylogenie der Insekten," Jenaische 

 Zeitschr. x., 1876. 



X A. Tichomirow, ' Entwicklungsgeschichte des Seidenspinners im 

 Ei ' (Moskau, 1882 : in Ptussian). 



§ Emery, " Keferat iiber die Arbeiten von Korotnew und Grassi," 

 Biol. Centralbl., Bd. v., 1887, pp. 056-657. 



II Kennel, "Entwicklungsgeschichte von Peripatiis," Arbeiten a. d. 

 zool.-zoot. Inst, in Wiirzburg, Bd. 7, 1885, pp. 95-200, Taf. v.-xi., Bd. 8, 

 1888, pp. 1-93, Taf.i.-vi. 



