Development of the Sexes in Lisects. 207 



are produced by the formative power from the fluid of the 

 Q^g are, a nervous system, a muscular system, an air-vessel 

 system, and an alimentary system, together with the salivary 

 and biliary vessels belonging to the latter, — also a pair of 

 excretory organs (namely, the spinning- vessels) , a dorsal 

 vessel, and, lastly, the germs of undeveloped reproductive 

 organs, with Sb perfectly distinctly visible distinction of the two 

 sexes. On the fifth plate of the above-mentioned work he 

 gives an exceedingly instructive and true view of the germs 

 of the reproductive organs of both sexes, as these gradually 

 enlarge from the first formation of the cabbage-caterpillar in 

 the Qg^ up to its full growth and approach to transformation. 

 In fig. 1 he shows the two reniform corpuscles divided by 

 three constrictions into four sections lying one behind the 

 other (the futm-e testes), with two filaments issuing from them 

 laterally (the future efferent ducts), from a male caterpillar 

 which had crept out of the Qgg a few hours before ; whilst in 

 fig. 2 of the same plate we may recognize the two bud-like 

 corpuscles, with four laterally approximated sausage-like 

 divisions and two fine filaments springing from behind, as the 

 future ovaries and oviducts of a female caterpillar of similar 

 age. I will not, however, conceal that Hermann Meyer, of 

 Zurich, did not succeed* in finding the sexual parts in cater- 

 pillars which were only a few days old ; on the other hand, 

 Weismann, in his remarkable work on the embryology of 

 insects t completely afiirms the correctness of the observations 

 first made by Herold in butterflies of the occuiTcnce even in 

 the embryo of the germs of the sexual glands with distinctly 

 visible distinction of the sex, inasmuch as he could likewise 

 distinguish the rudiments of the sexual glands in the embryos 

 of flies in the Qgg^ although the difference between the germs 

 of the male and female sexual glands is much less striking. 

 In the investigation of a Tipulide larva, however, Weismann 

 obtained other results, which I must not pass over. When he 

 sought the genital glands in the embryos of Corethra plumi- 

 cornis\^ he certainly convinced himself that in this insect also, 

 as in the larvae of the true flies, the sexual glands are already 

 traced out in the embryo ; but he found that in the larvae of 

 Corethra just escaped from the ^gg the distinction is as yet 

 by no means clear, and this distinction does not make its 



* "Ueber die Entwickelung des Fettkorpers, der Tracheen und der 

 keimbereitenden Geschlechtstheile bei den Lepidopteren," Zeitsch. fur 

 wiss. Zool. Bd. i. p. 177. 



t " Die nachembryonale Entwickelung der Musciden nach Beobacb- 

 tungen an Musca vomitoria und Sarcophaqa carnariar ibid. Bd. xiv. 

 p. 219. 



X Die Metamorphose der Corethra plumicornis, ibid. Bd. xvi. p. 99. 



15* 



