428 Miscellaneous. 



fluid pass in the direction this hypothesis postulates ; that is, from 

 the blood-vessels, into the pericardium. 



Similar improbability attaches to a view which supposes a fluid of 

 such chemical and such morphological characters as the blood of the 

 Lamellibranchiata to suffer dilution to such an extent as the ob- 

 servable distention of their foot would necessarily imply, and which 

 argues from phenomena noticed on the sudden removal of the animal 

 from the water as though they could be regarded as identical with 

 normally occurring physiological processes. 



As their injections seem to them to prove the existence of a system 

 of vessels distinct from and yet in most close apposition to the blood- 

 vessels and permeating the several tissues of the body in company 

 with them, the facts of the case seem to the authors to necessitate the 

 belief that a transference of fluid takes place, as in other organisms, 

 from the latter to the former set of vessels. 



The animals experimented upon were Unionidce of the two species 

 Anodonta Cygnea and Unio margaritifera. 



MISCELLANEOUS. 



On the Larval state of the Muscidae. By Rud. Leuckart. 



It is, I think, a very general opinion that, up to their change into 

 pupae, the headless larvae of the flies are subject only to such changes 

 as are brought about by their growth and the formation of their 

 generative organs. Wherever any other differences were observed 

 between the newly-hatched and full-grown larvae, as in the CEstridce 

 (Joly) and the Pnpipara (Leuckart), these have hitherto been re- 

 garded as exceptional cases. 



This view is erroneous. Investigations which I made in the 

 course of last summer upon the development of various Muscidce 

 render it probable that the animals belonging to this group in 

 general, like the above-mentioned CEstridce and Pnpipara, present 

 several different larval forms. The differences of these larval forms 

 do not, indeed, extend so far as to lead one to mistake their genetic 

 relations, but they are nevertheless sufficiently striking to fix the 

 interest and attention of the naturalist. 



The differences of these larval forms are most distinctly indicated 

 in the formation of the buccal organs and of the stigmata. Reserv- 

 ing further particulars for a future communication, I will in the fol- 

 lowing only indicate in a few words the chief differences of the three 

 larval states observed by me in Musca vomitoria and M. ccesarea. 



First stage (duration in summer about twelve hours). — Anterior 

 stigmata wanting. The truncated posterior end bears on each side 

 two closely approximated, cleft-like air-holes. The oral opening, in 

 repose, is a triangular pit, the lateral edges of which converge in 

 front and bear a chitinous ridge, at the anterior extremity of which 

 a number of small teeth follow. When the mouth is opened, the 

 lateral horny ridges separate at their anterior extremity. The pos- 



