78 Miscellaneous. 



The pond in which this was found is a very small One, only 5 or 6 

 yards in diameter, and the only other species I have met with in it 

 is Lophopus crystaUmus ; of the latter I have not met with any this 

 year. This variety grows attached to twigs in the full blaze of the 

 sun; and the little animals appear to enjoy it immensely. The speci- 

 men I obtained was about four inches long, by an inch thick in the 

 middle ; but I left another about the same length but apparently 

 thicker. 



I am, Gentlemen, 



Yours obediently, 

 Devon and Exeter Institution, Ebwaed Paefitt. 



Exeter, June 18^ 1868. 



On the Avicolar Sarcoptidce, and on the Metamorphoses of the Acanna. 



By C. Robin. 



The Acarina pass through a series of metamorphoses — a hexapod 

 larva issuing from the egg becoming converted into a nympha, from 

 which the adult Mite proceeds. The author has observed in the 

 Sarcoptidae a more complicated series of phenomena ; in these the 

 males pass through four, and the females through five stages, indi- 

 cated as follows :— 



1. The egg, on issuing from which the animal has the form of 



2. A hexapod larva, followed by the stage of 



3. Octopod nymphce without sexual organs. 



4. From some of these nymphae issue : — a, sexual mates, after a 

 moult which is final for them ; h, from others issue females without 

 external sexual organs, resembling the nympha), but larger, and in 

 some species furnished with special copulatory organs. 



Finally, after a last moult following copulation, these females 

 produce 



5. The sexual and fecundated females, which do not copulate, and 

 in the ovarj^ of which eggs are to be seen. No moult follows that 

 which produces males or females furnished with sexual organs ; but 

 previously to this the moults are more numerous than the changes 

 of condition. 



Ovular and embryonal state. — The eggs of these Acarina are of a 

 cylindroid form with rounded ends, one of which is smaller than the 

 other, and corresponds with the rostrum. They arc more or less 

 flattened on one side ; and to this surface the ventral surface of the 

 young animal corresponds. The exclusion is eff'ectcd by the division 

 of the cephalic extremity into two halves. The ova are deposited 

 by the avicolar Sarcoptidoe in the angle formed by the barbs with 

 the stem of the feather. In general the segmentation of the vitcllus 

 has not commenced when the eggs are laid ; but in some species the 

 vitellus is divided into four lobes while the egg is still in the oviduct* 

 The division takes place in planes perpendicular to the greater axis 

 of the vitellus. 



The Larva. — In all the species the larva? are hexapod ; and the 

 arrangement of the epimera shows that it is the third, and not the 



