j^ Mr, CuRTis's Obfervaiions on j^phides, 



large or choice colledion be viewed, when there is fcarccly a plant 

 but what exhibits fymptoms of difeafe occafioned by vermin ? 



As the fpccies of this genus are very numerous, and afford but 

 few marks of diftindion, Linnasus has contented himfelf with giv- 

 ing mofl of them trivial names, according to the particular plant 

 on which they are found : a clofe attention to them \\ill, however, 

 difclofe more diftinctive characters than naturalifts are aware of. - ~ 



j^phides are defcribed by the beft informed authors as being gene- 

 rally oviparous and viviparous at different periods of the fame year. 

 Monf. Bonnet, who had the honour of making tbis difcovery in 

 174O*, fays that in the fummer the females are viviparous, but 

 toward the middle of autumn they lay real eggs. De Geer obferves, 

 that the females of all the Aphides he had fcen, conflantly laid eggs, 

 intended to prcferve the fpecies during winter, and that he is 

 therefore inclined to believe that the fame takes place in all Jphides 

 whatever. From the 24th of September to the 6th of December 

 following, during which time Fahrenheit's thermometer had been 

 as low as 29, I found the jiphis falicis to be conftantly viviparous, 

 though from the inclemency of the weather very few of thefe in- 

 fects at the period laft mentioned remained on the trees, and 

 thofe few were foon after entirely cut off by the unufual cold that 

 took place, the thermometer falling to 4 degrees below o. — Other 

 Aphidis are oviparous or viviparous according to the temperature of 

 the air to which they are expofed. In very cold weather they are 

 oviparous, for this obvious reafon : the eggs are capable of refilling 

 cold more powerfully than the young. On the 2 2d of November 

 fame year as above, I found a confiderable number of eggs which 

 had been depofited in fome auricula plants by a fmall green Aphis^ 



• Or rather Monf. Trembley, See his Letter to M. Bonnet from the Hague : Oeuvres 

 4c Bonnet. ' . 



which 



