384 THE AXATOMY OF LXVERTEBRATED ANIMALS. 



feet fertilizable female, by little more than their smaller size, 

 and that they possess completely developed female organs. 

 These neuters, or rather, small females, laid eggs which de- 

 veloped, and gave rise only to male JPolistes. The unim- 

 pregnated females of a Saw-fly, Nematus ventricosus (the 

 larvae of which are known as gooseberry caterpillars), regu- 

 larly lay eggs, which develop and produce male offspring. 



The terms arrenotokous and thelytokous have been pro- 

 posed by Leuckart and Von Siebold to denote those par- 

 thenogenetic females which produce male and female voung 

 respectively. 



In the case of the Hive-bee, it has been ascertained that 

 the queen either impregnates, or does not impregnate, the 

 eggs when they are laid. The sj)ermatheca, in which the 

 spermatic fluid, introduced by the single act of copulation 

 which takes place, is contained, contracts as the eggs pass 

 along the vagina, in the former case, and remains passive in 

 the latter. The unimpregnated eggs give rise to males or 

 drones ; the impregnated eggs to females, which become 

 neuters with imperfect reproductive organs, or queens, with 

 perfect organs, according to the nutriment which they re- 

 ceive. 



In the Aphides, ova deposited by the impregnated females 

 in the autumn are hatched in the spring, and give rise to 

 forms which are very generally wingless, and bring forth 

 living young. These may be either winged or wingless, and 

 are also viviparous. The number of successive viviparous 

 broods thus produced has no certain limit, but, so far as our 

 present knowledge goes, is controlled only by temperature, 

 and by the supply of food. Aphides kept in a warm room 

 and well supplied with nourishment have continued to propa- 

 gate viviparously for four years. 



On the setting in of cold weather, or, apparently, on the 

 failure of nourishment alone, in some cases, males and females 

 are produced by the viviparous forms. The males may pos- 

 sess wings, or may be devoid of them. The females appear 

 invariably to be apterous. Copulation takes place and the 

 eggs are laid. 



Sometimes viviparous forms coexist with the male or fe- 

 male forms, and some viviparous Aphides are known to hi- 

 bernate. 1 



1 Huxley, " On the Agamic Reproduction and Morphology of Aphis." 

 (" Linnsean Transactions," 1857.) 



The papers of M. Balbiani (" Ann. des Sciences Naturelles," 1869, 1870, and 



