Development of the Sexes in Insects. 207 
are produced by the formative power from the fluid of the 
egg 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 a 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 egg 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 future testes), with two filaments issuing from them 
laterally (the future efferent ducts), from a male caterpillar 
which had crept out of the egg a few shours 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} completely affirms the correctness of the observations 
first made by Herold in butterflies of the occurrence 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 egg, 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- 
cornist, he certainly convinced himself that in this insect also, 
as in the larve of the true flies, the sexual glands are already 
traced out in the embryo; but he found that in the larve of 
Corethra just escaped from the egg 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. fiir 
wiss. Zool. Bd. i. p. 177. 
+ “Die nachembryonale Entwickelung der Musciden nach Beobach- 
tungen an Musca vomitoria und Sarcophaga carnaria,” ibid. Bd. xiv. 
210. 
: t Die Metamorphose der Corethra plumicornis, ibid. Bd. xvi. p. 99. 
15? 
