40 Rece?it Literature. [January, 



fly is most abundant in rather wet and moderately warm seasons ; 

 while warmth appears to be the chief element in developing the 

 Aphides or plant lice, some species being more favored by a humid 

 atmosphere, while others develop more rapidly in a dry season. 

 " The cut-worms are developed more abundantly in such seasons as 

 increase the army-worms, which in their normal habits are but cut- 

 worms, massing in armies and migrating being really an abnor- 

 mal condition in their history. Observation shows, as heretofore 

 stated, that, as a general rule, those species which occasionally 

 develop in such vast numbers require for this purpose two con- 

 secutive seasons, though the character of the seasons for the dif- 

 ferent species differ somewhat. That is to say, those which bring 

 out one species are not the ones which bring out another. As 

 examples of the correctness of this statement I have only to refer 

 to the migratory locusts, the chinch bug, as heretofore shown, 

 the Hessian fly, the army-worm, etc. The locust and the chinch 

 bug require the same kind of seasons, that is, two successive dry 

 years, the latter warm as well as dry ; consequently, when two 

 such seasons prevail generally over the Northwest, both species 

 are apt to appear, as was the case in 1X74. But the case is differ- 

 ent with the army-worm. This requires a dry summer and fall, 

 and I am inclined to believe also a dry winter, followed by a cool 

 and rather damp and cloudy spring. The two most noted years 

 of its appearance in this State were 1861 and 1875, each of which 

 followed a preceding dry year, but in neither case was the year 

 in which it appeared warm, 1861 being one of average tempera- 

 ture, and 1875 rather cold. The latter, which is the only one for 

 which we have the records of the different seasons, was more 

 than usually damp in the spring and summer." Some meteoro- 

 logical tables are given in illustration. 



These chapters are followed by a descriptive catalogue of larva; 

 that of the caterpillars of butterflies being compiled by Miss Net- 

 tie Middleton, that of the Sphingidae, yEgeridae and Bombycidae 

 by Mr. John Marten, while a chapter giving original notes on 

 caterpillars is contributed by M. D. VV. Coquillet. The Report 

 closes with a reprint of Bulletin 4 of the U. S. Entomological 

 Commission on the Hessian fly, by A. S. Packard, Jr. 



Walcott os the Organization of Trilobites. 1 — In this essay 

 Mr. Walcott brings together the results of much patient labor in 

 preparing sections and studying them with a view to settle the 

 vexed question as to the nature of the limbs of the trilobite. 

 The results are as follows : No antennae have been discovered ; 

 but " four pairs of manducatory jaws, formed by the basal joints 

 of the four anterior pairs of appendages," which " have a general 

 'lar to the cephalic legs of Limulus and Eurypterus." 



• New and old evidence relating t> [f> organization. By C. D. 

 Cambnd-e. March, 1 88 1. 



