INSECTA. 613 



In a genus Goccina (Dorthesia), several species of which 

 are found in this country, the female — although apterous 

 and active in all stages — is completely covered with a 

 snow-white secretion, which gives it more the appearance 

 of a little plaster-cast than anything else. 



In another tribe, the Phytophthiria, both sexes are 

 either wingless or furnished with four distinctly veined 

 wings. The rostrum springs apparently from the breast ; 

 the tarsi are two-jointed, and furnished with two claws. 

 The most familiar species of this tribe are the Aphides, 

 Plant-lice, which have ever been regarded with consider- 

 able interest by the naturalist. Their bodies . are flask- 

 shaped, and furnished with six feet, a pair of antenna?, 

 and very generally with a pair of short tubes close to the 

 extremity of the abdomen, from which a clear sweet 

 secretion exudes. Both sexes are at one period winged, 

 at another wingless ; and individuals of the same species 

 are often winged and apterous at different periods of the 

 year. Perhaps the most remarkable phenomena in the 

 history of generation was first observed in the Aphis, and 

 to which great significance has been given by Professor 

 Owen, under the name Parthenogenesis or virgin-procre- 

 ation. This mode of generation is not confined to insect- 

 life, the same has been observed in the Salpce among 

 mollusca, the Distomata among entozoa, each parent giving 

 birth to an embryo different to itself; and this embryo 

 living as an independent animal, gives birth, without inter- 

 course, to another and to a successive series, until at length 

 a progeny is formed bearing the likeness of the first parent. 

 In the Aphis the ova are deposited by the parent insect, 

 and in due time produce larval wingless Aphides. Each 

 virgin Aphis of this brood will produce other similar 

 broods without intercourse ; this will go on to the 

 eleventh generation, the last generation being winged, and 

 male and female : these have intercourse, and then com- 

 mence the same series of phenomena over again. 



The Maple-aphis, better known as the Leaf Insect 

 (Plate VI. No. 128), averages about the one-fiftieth of 

 an inch in length, and, although long sold and exhibited 

 under the name of the "Leaf Insect," nothing was 

 known of its origin and history, with the exception of 



