68 



Americanus,) in which last he ascertained that three generations 

 are produced from one impregnation. 



" On the luminous spots of the great Fire-Fly of Cuha.^'' 



" Observations on the Seventeen-year Locust.^^ 



** On Spermatozoa.^^ 



" On the origin, development, and structure of the Kidneys 

 throughout the vertehrated division of animals.'''' 



" Notes on the Rattle-snake, relating to its dentition, to the 

 physiological effects of its poison, and to alcohol as a remedy.^'' 



" Some account of an Insect, (Rhinosia pometella, Harris,) and 

 its recent injuries to the fruit and forest trees of New England.'''* 



" On the development of Viviparous Aphides, or plant lice.'''' 

 This is a subject of great interest, and it was investigated with 

 great ability. Since the days of Bonnet, it has been well known 

 that several successive generations of Aphides are produced after 

 a single impregnation. Dr. Burnett studied the successive gene- 

 rations as they first appear in the body of the parent as illus- 

 trated by the species infesting the hickory. If a fully developed, 

 but wingless Aphis is examined in the spring, it is found to con- 

 tain an embryo nearly mature ; and this embryo contains already 

 the first germs of the third generation, in the form of single cells 

 or a small number of cells inclosed in a sac. While a few germs 

 are thus formed, others are formed by their subdivision from con- 

 striction, until the requisite number is obtained. When they 

 have reached the size of about one three-hundredth of an inch, 

 a yellowish mass forms at one extremity of the egg, and then 

 commences the development of the parts of the insect, which 

 eventually inclose the mass just mentioned. It is this last yellow- 

 ish mass which furnishes the materials for the next generation. 

 All this, it should be remembered, is effected without the aid of 

 any distinct reproductive organs. There is no ovary or oviduct, 

 but the embryos are developed in the cavity of the abdomen, 

 and discharged through a genital opening merely. In view of 

 the fact that the viviparous aphides are sexless. Dr. Burnett re- 

 garded their mode of reproduction as belonging to the gemmipa- 

 rous type. Viewed in this way, the different broods cannot be 

 looked upon as so many generations ; but on the contrary, the 

 whole suite, from the first to the last, that is, till the production 



