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TEXT-BOOK OF ENTOMOLOGY 



A 



the posterior intestine and apparently derived from the same blastems or buds 

 as the latter. 



Uljanin studied these organs in the larva of the honey-bee. They are two 

 renifonn bodies in the middle of which will soon appear the ovarian tubes. 

 They also give birth to the internal parts of the excretory ducts, while the ex- 

 ternal part of the genital tube, as also the accessory glands which are connected 

 with it, are derived by an invagination of the hypodermis at the surface of the 

 penultimate segment. 



Dohrn observed in the larva of ants the rudiments of the ovaries in the form 

 of two pyriform masses, each with eight prolongations which he regarded as 

 young ovarian tubes. 



In Kncyrtus Bugnion observed the rudiments of the sexual glands in the 

 middle of the larval period ; they were rounded and with no apparent con- 

 nection with the neighboring 

 organs. Afterwards these 

 rudiments elongated, ap- 

 proached nearer to the ventral 

 surface, and placed themselves 

 in relation with some small 

 cell-groups which appeared 

 under the rectum, and seemed 

 destined to form the efferent 

 canal (vas deferens) and ac- 

 cessory glands of the genital 

 organs. He thought the sex 

 could be recognized in the 

 second half of larval life, the 

 male gland being distinguished 

 by its rounded shape and 

 smaller size ; the ovary by its 

 oval form and larger size. In 

 A larvae ready to be transformed 

 the testis formed a cellular 

 mass enveloped by a cuticle, 

 and at its hinder end pro- 

 longed into an epithelial cord, 

 which is undoubtedly the vas 

 deferens. The ovary -had a 

 similar envelope, and from its 

 cellular mass arose epithelial cords which were destined to become the ovarian 

 tubes. 



FIG. 552. Three longitudinal sections through the em- 

 bryo of Chironomus. In A, the blastoderm (bl) is begin- 

 ning to form, the polar cells (p) outside of it; in , the 



polar cells have pressed in between the blastoderm cells ; in 



C, they lie in the interior of the embryo : b, p 



layer (Keimhautblast) ; d, yolk ; k, nucleus of the forming 



C, they lie in the interior of the embryo : b, protoplasmic 

 layer (Keimhautblast) ; d, yolk ; k, nucleus of the for 

 blastoderm. After Hitter, from Korschelt and Heider. 



m. Length of embryonic life 



The duration of embryonic life varies greatly in different insects. 

 The embryo of the blow-fly is fully developed in less than 24 hours, 

 that of the house-fly in 24 hours. In the locusts and tree-cricket 

 the embryos begin to develop at the end of the summer, continuing 

 to grow until the cool weather of autumn, when growth is arrested, 

 the later stages being finished in the latter part of the spring. It 

 is so, likewise, with the embryos of many moths and other insects. 



