598 



ZOOLOGY 



SECT. 



vasa deferentia uniting to form a median ejaculatory duct. A 

 vesicula seminalis is appended to each vas deferens or to the 

 ejaculatory duct. Accessory glands, opening into the vas deferens 

 or the ejaculatory duct, secrete cementing material for uniting the 

 sperms into masses, the spermatophores. In most instances the 

 eggs are laid shortly after their fertilisation, only a few forms, such 

 as the Aphides or Plant-lice, many Diptera, and some Coleaptera, 

 being viviparous. Some Insects, such as the Aphides and Bees 

 and Wasps, as well as some Lepidoptera and Neuroptera, present 

 us with the unusual phenomenon of parthenogenesis ; i.e. ova are 

 formed, as in ordinary female insects, in organs corresponding to 



Fio. 488. A, female ; B, male sexual apparatus of the Honey-bee; ad, accessory glands ; e?, 

 common ejaculatory duct ; gd, poison glands ; gb, poison vesicle ; A's, bulb of the stinging 

 apparatus ; md, rectum, twisted back and cut off ; lira, accessory sac of the vagina (bursa 

 copulatrix) ; oil, oviduct ; p. penis ; rs. receptaculum seminis ; sd, colleterial gland ; t. testes ; 

 i-(j. vagina ; rd, sperm ducts. (From Lang's Comparative Anatomy.) 



the ovary of the latter, and these are developed without fertilisa- 

 tion. In the case of the Aphides, an autumn generation of 

 completely developed males and females is followed by a spring 

 generation consisting entirely of females; these are both par- 

 thenogenetic and viviparous. In the Bees, the workers (imper- 

 fectly developed females) occasionally produce ova which, without 

 fertilisation, develop into drones (males). In one or two groups, 

 including the Scale-Insects (Coccidce) and Gall-Insects (Cynipidai), 

 males are never developed, so that reproduction is exclusively par- 

 thenogenetic. Pcedogenesis accompanies parthenogenesis in certain 

 Diptera ; i.e. the larvae produce ova and embryos without impreg- 

 nation. 



The eggs when laid are protected from injury by a number of 

 methods ; they may be firmly fixed to the substratum, buried in 



