200 



it passes into the chrysalis state. The wings are long enough to 

 extend half the length of the perfect insect. The posterior pair 

 are membranous bags, somewhat flattened like the respiratory 

 vesicles of marine worms, with distinct ribs, which are blood 

 vessels. The anterior pair are also bags with their upper half 

 stiff and inflexible like the elytra of Coleoptera. The legs are 

 tubular, but not jointed as in the perfect insect, and are bent 

 backwards. The jaws are changed into two long tubes, which 

 are bent backwards, as are also the antennae. In the chrysalis 

 the wings are flattened and soldered together, as are the legs and 

 sucking tubes. The order of development of the different parts, 

 and the coleopterous condition at an incomplete stage, show that 

 naturalists have been in error in placing chewing insects, as 

 the Coleoptera, above the sucking insects. The order should be 

 reversed. These observations may be confirmed by examining 

 specimens just at the moment when the skin begins to split on 

 the back. Prof. Agassiz exhibited drawings illustrating all the 

 conditions described. 



Dr. Gould presented descriptions, and exhibited drawings 

 of several new species of the naked niollusks of the vicinity 

 of Boston. 



Mr. Desor communicated some observations made by Mr. 

 Whitney and himself in reference to the probable origin of 

 the so-called fossil rain drops, which, in this country, are 

 found on slabs of New Red Sandstone, as well as Potsdam 

 Sandstone. 



He said it had already been noticed by Mr. Teschemacher that 

 these so-called rain drops, when closely examined, are found to 

 differ in several respects from the impressions made by the rain 

 on a beach, where each drop produces an impression surrounded 

 by a rough crest, more or less elevated according to the force of 

 the rain. The fossil impressions on Sandstone, on the contrary, 

 are generally flat and smooth. Besides, there is hardly a shower 

 in which the rain drops are not numerous enough to cover the 

 whole or nearly the whole ground, whereas the fossil impres- 

 sions are generally scattered and so few in number that it seems 

 almost impossible to ascribe them to rain. 



Mr. Desor said, that whilst encamped on the border of Lake 



