NOTES AND MEMORANDA. 417 



veritable metamorphoses ; when the larva is on the point of passing 

 to its second stage, it becomes altogether inert, all the internal 

 organs become resolved into a semi-fluid substance, which envelops a 

 kind of blastodermic memhrane, which behaves exactly as the blasto- 

 derm of the eggs, and gives rise to swellings which develop into 

 new appendages, and which are themselves arranged just as are 

 the appendages of the developing larva ; soon casting its envelope, a 

 new and larger Acarus appears, but the rejected envelope exhibits all 

 the former organs of the larva, empty and discoloured ; this curious 

 rejuvenescence may be effected in the space of twenty-four hours. 



In the normal course these changes, the essential characters of 

 which are the same in all moults, pass through the following cycle : 

 ovum, larva, normal nymph, sterile female, ovigerous female. "When 

 the course is altered in any way, the form in most cases dies down at 

 once, but there are certain species which escape, thanks to a method 

 to which M. Megnin, its discoverer, has given the name of adventitious 

 metamor pilosis. 



This is what occurs with Pterolichus falciger, a form which infests 

 pigeons ; when the pigeon moults with great rapidity, and loses nearly 

 all its feathers, the normal nymph, instead of becoming a male or 

 sterile female, gives rise to a worm-like form, and passes to the 

 cellular or peritracheal tissue, which is especially loose in these 

 birds ; here it lives for a time and increases in size, passing again 

 towards the integumentary tissue only when the ordinary conditions 

 of its existence are re-established. It was apparently forms in this 

 stage which fell under the observation of Messrs. Kobertson and 

 Filippi. 



After a description of acarine parasites of the gallinaceous birds, 

 M. Megnin gives an account of the form found in the air-cavities ; this 

 specimen does not appear to belong to the Sarcoptidce, but to be tho 

 representative of a new group, of which it is at present the only known 

 genus ; M. Megnin finds that it is provided with a conical rostrum, 

 which is perforated anteriorly, and which is formed by the fusion of 

 the maxillae, the labial palps, and the mandibles ; he names it, on 

 account of its mode of life, CytoleicJius {kvt6<; = cavity, and Aei'^oj = 

 lick up) ; living as it does on the walls of the cavities which it 

 inhabits, it does not seem capable of producing any inflammation of 

 these parts. The species has, on account of its form, the name Sarcop- 

 toides ; it is described as ovoviparous, and an account is given of its 

 male, young female, nymphs, octopod and hexapod larvae. The form 

 is found in the air-sacs of the Gallince, and especially of the Pliasia- 

 nidce, where it lives in colonies ; the individuals are of a relatively 

 large size, and of a white colour. It is only dangerous in excess, 

 when it may produce cough, and, perhaps, asphyxia. 



On some Genera of Acarina. — Haller's two papers on this subject * 

 are reviewed by Megnin ; "j" the first is a revision of the genus Analjes 

 (^Dermaleichus). It may be interesting to note the earliest observations 



* 'Zeitsch. f. wiss. Zool.' (1877). 



t ' Joiu-ii. Anat. ot Pliys.' (Robin), xiv. (1878) 107. 



VOL. II. 2 E 



