166 Miscellaneous. 



constituted by a development or transformation of the corresponding 

 parts of the larva, but by a new formation. 



We have detected a curious adaptation to their mode of life in the 

 larvje of the Volucellce. One species lives in the nests of hornets, 

 another in those of the common wasps, and another in the nests of 

 humble-bees ; a special armature secures to each of them an easy 

 progress upon the particular substance of which each of these nests 

 is constructed. When adult, the Volucellce seem to have borrowed 

 the clothing of the hornets, wasps, or humble-bees, in order to come 

 and lay their eggs in the habitations of those insects. 



In the nervous system of the Volucellce we have observed remark- 

 able transformations. The very general character of the nervous 

 system of insects in course of development is, to affect in the larvae 

 the form of a long ganglionic chain, undergoing a more or less con- 

 siderable abbreviation as the animal advances in age. This abbrevia- 

 tion takes place in the connectives, and induces the fusion of several 

 ganglia. On the contrary, in our Diptera, in the larva state, the 

 nervous centres are approximated and so intimately united that they 

 only form a single mass ; with advancing age a separation is effected 

 between the nervous centres of the head, thorax, and abdomen, at 

 the same time that long connectives are formed uniting the meduUary 

 masses to each other. The important fact to be noted is, that this 

 observation must modify the too general idea which has been con- 

 ceived with regard to the changes which the ganglionic chain under- 

 goes in the period of transition from the state of larva to the adult 

 state. 



On another hand the change of diet of our Volucellce on passing 

 from one form to the other offered us a subject of investigation of 

 high interest. The larvae of the Volucellce are carnivorous ; the 

 adults live upon pollen : the diet corresponds to the differences 

 presented by the digestive apparatus in the two states. The larva 

 has no receptacle for food ; the adult, on the contrary, is furnished 

 with an ample crop : the former, having an abundance of nourishment 

 always within its reach, has no abstinence to fear; for the adult, which 

 is often prevented from seeking its nourishment by atmospheric 

 conditions, an alimentary receptacle becomes very useful. 



The salivary glands of the larvae are enormoiis : the diet of the insect 

 having to change, a transformation of its glands is effected during the 

 pupal period ; they are in part destroyed, to be afterwards regenerated 

 with a different histological constitution. In the adult they have 

 acquired the form of slender tubes, which extend into the thorax 

 and abdomen. Equally great modifications take place in the same 

 way in the four appendages of the stomach — long caecal tubes, which 

 are replaced by four conglomerated glands. 



With regard to the respiratory apparatus, we must also cite some 

 of the results of our observations. It affects a special character 

 in each phase of the life of the insect. In the larva we find four 

 stigmata — two anterior, on the second segment, and two posterior, on 

 the twelfth segment. When the animal is metamorphosed, the 

 integument separates from the skin of the larva, the orifices for the 



