200 BOARD OF AGRICULTURE. 



above, the head somewhat triangular or crescent shaped, the pro- 

 thorax is large and of the same width as the body, and the legs are 

 thickly spiued. 



Aphidae. Every thing about this extensive group is of the 

 greatest interest, whether it be their structure, mode of growth 

 or habits and relations to other insects. They have soft oval 

 bodies, with two slender tubercles behind, with somewhat square 

 heads and long slender seven-jointed antennae. The beak is often 

 half as long as the body. They are generally colored green, and 

 often have a soft bloom upon the surface. " The brief history of 

 the general conditions of the development of these insects is as 

 follows : — In the early autumn the colonies of plant-lice are com- 

 posed of both male and female individuals ; these pair, the males 

 then die, and the females begin to deposit their eggs, after which 

 they die also. Early in the spring, as soon as the sap begins to 

 flow, these eggs are hatched, and the young lice immediately begin 

 to pump up sap from the tender leaves and shoots, increase rapidly 

 in size, and in a short time come to maturity. In this state it is 

 found that the whole brood, without a single exception, consists 

 solely of females, or rather, and more properly, of individuals 

 which are capable of reproducing their kind. This reproduction 

 takes place by a vivipax'ous generation, there being found in the 

 individuals in question, young lice, which, when capable of enter- 

 ing upon individual life, escape from their progenitors, and form 

 a new and greatly increased colony. This second generation per- 

 Bues the same course as the first, the individuals of which it is 

 composed being, like those of the first, sexless, or at least without 

 any trace of the male sex throughout. These same conditions are 

 then repeated, and so on almost indefinitely, experiments having 

 shown that the power of reproduction under such circumstances 

 may be exercised, according to Bonnet, at least through nine gen- 

 erations, while Duvau obtained thus eleven generations in seven 

 months, his generations being curtailed at this stage not by a 

 failure of the reproductive power, but by the approach of winter; 

 whicli killed his specimens ; and Kyler even observed that a colony 

 of Aphis Dianlhi, which had been brought into a constantly heated 

 room, continued to propagate for four years in this manner, without 

 the intervention of males, and even in this instance it remains to 

 be proved how much longer these phenomena might have been 

 continued." Dr. Burnett, fi'om whom we quote, considers this 



