INSECTS. 271 



individuals occur, which being incapable of propagating have been 

 commonly considered to be sexless (the so-called neuters, working- 

 bees, &c.) Even the external form indicates that they resemble 

 rather the female than the male individuals, as the same is also 

 indicated by their mode of life and their instinct directed to the care 

 of the young ones. Anatomical investigation has confirmed this 

 conclusion by demonstrating in the working-bees imperfect ovaries 1 . 

 These individuals thus remain imperfect females, nurses, foster- 

 mothers. 



Observations are not wanting with respect to the development 

 of Insects in the egg, although hitherto this subject has not been 

 sufficiently investigated to allow a general representation of it to be 

 offered. In eggs that are just laid, nay in those which lie at the 

 owest part of the oviduct and are the most mature, the germinal 

 vesicle has disappeared ; in eggs situated higher up in the oviduct 

 it may be seen clearly with the germinal spot 2 . On the yelk is 

 'ormed, from a union of cells, a layer as germinal membrane (blasto- 

 derma) which continues to grow so as to surround the entire yelk. 

 The first rudiment of the embryo, the nota primitiva, lies on the 

 ventral surface ; the yelk lies on the dorsal surface, and becomes 

 enclosed by the constantly growing ventral plates, without the for- 

 mation of a special umbilical- or yelk-sac by constriction. The 

 stigmata are developed only at a late period, and become open only 

 shortly before the escape from the egg 3 . 



1 MADEM. JURINE in HUBEB Nouv. observations sur les Abeilles, IQ e*dit. Paris et 

 Jeneve, 8vo. II. Tab. xi. fig. i, figure copied by RA.TZEBURG in his enquiries on this 



subject in Nov. Act. Acad. Cces. Leop. Car. Vol. xvi. PI. u. Tab. 47. 



2 See the microscopic representation of an egg-tube from Agrion, by R. WAGNER, 

 Abhand. der mathem. physic. Klasse der Akademie in Miinchcn, Bd. II. fig. I ; see 

 s. 558. 



3 On the development of insects in the egg there are some observations of SDCKOW, 

 Analomisch-physiologische Untersuchungen der Insecten und Krustenihiere, Heidelberg, 

 1818, 4to. mit Kupf. s. 19, 23, 35 (eggs of Bonibyx pini); also short, but interesting 

 communications by RATHKE, on Blatta germanica in MECKEL'S Archiv. 1844, s. 27 

 37, Taf. n. (here there is on each side of the abdomen in the embryo, behind the attach- 

 ment of the third pair of feet, a pediculated disciform organ which is, perhaps, a tem- 

 porary respii'atory organ to be compared with the gills of larvae of salamanders ; there 

 are only four Malpighian vessels, which are increased in number after birth), and 

 finally, by KOELLIKER (on Chironomus, Simulia, Donacia) Observationes de prima 

 Insectorum genesi Diss. inaug. Adjectce sunt in. Tabul. Turici, 1842, 4to. The numerous 

 plates of HEROLD in his Disquisitiones de Animalium vertebris curentium in ovo 



