SCIENCE GOSSIP. 



363 



im llic wmc liacki^rinind— ihus ri'iircxluiinu in another 

 rlircctioii '.hi; case of the hcd(;c-s|)nrri)w and robin. 



I take exception to Mr. Hughes's statement that 

 only the et;i;!< of bird.s which nest on the (ground arc 

 liable to be stolen. The jay and crow are both 

 inveterate thieves of the eggs of birds which nest in 

 hedges, trees, and thickets, and there may be other 

 offenders in this direction, although these are the only 

 ones of which I have actual proof. In other countries 

 serpents would probably lie nunibereil amongst the 

 aggressors. 



By the way, Mr. Hughes adduces several instances 

 of protective coloration, some of which had not 

 previously occurre<l to me. Some of the while-egged 

 species had even prejudiced me against the theory ; 

 but Mr. Hughes says most nocturnal species lay white 

 eggs. Is not this because their eggs are not likely to 

 be exposed to enemies by day, as the parents only 

 desert their nests after dark, when protective colour, 

 ing would be unnecessary ? Some birds, also, which 

 lay white or spotless eggs, cover them when leaving 

 the nest. Protective colouring is admitted in the 

 case of several species nesting on the ground, espe- 

 cially that of the nightjar, although I think Mr. 

 Hughes cannot fairly place its egg beside that of the 

 robin as a test, because one of the two would have to 



be removed from its natural environment. Although 

 the nightjar is a nocturnal bird, its eggs rei|uire pro- 

 lection, because they are laid on the ground and ex- 

 posed to the depredations of small nocturnal mammals 

 unlikely to menace the species breeding in trees and 

 bushes. 



I do not contend that protective coloration ex- 

 plains everything, but probably it comes largely into 

 use ; and numerous cases will occur to all who arc 

 familiar with the nesting of birds. So many excep- 

 tions of a puzzling and contradictory nature also 

 occur that I am often led to doubt whether the so- 

 called "protective" instances are not often merely 

 accidental coincidences of colour and surroundings. 



In watching a large flock of birds feeding together 

 in a field to-day, this discussion occurred to my mind. 

 There were gulls, rooks, starlings, and lapwings, 

 which daily resort to the low-lying fields around here 

 for sustenance. Their food must be similar, probably 

 worms and grubs in every case. \'el here we have 

 represented olive-green, spotted blue, plain blue, and 

 stone-brown types of eggs, falling under three sepa- 

 rate classes of Mr. Hughes's arrangement, and not 

 with the uniformity that similar feeding should pro- 

 duce. No doubt other instances could be adduced. 



60 lioniliy Road, Walton, Liverpool. 



BRITISH FRESHWATER MITES. 

 By Charles D. Soar, F.R.M.S. 



{Continued /roiii page 338.) 



GENUS ATAX FABRICIUS, 1805. 



T T NDER this genus, there have been between 

 ^^ thirty and forty species described during the 

 present centur)- by dift'erent writers from various parts 

 of the world. In 1894 Piersig divided this genus 

 into two, retaining the name of Ala.x for one portion 

 and Cockkophorus for the other. Koenike does not 

 think Piersig had sufficient grounds to do this, so he 

 ignores the latter name ; and in his work on the 

 Hydrachnidae of Madagascar, published in 1898,' 

 places all the species of these two genera under 

 the one genus Alax. Mr. R. 11. Walcott, the 

 American writer on water-mites, thinks the differences 

 in the two genera above mentioned clearly defined, 

 and has accordingly adopted Piersig's suggestions. 

 .Vs I wish to follow Piersig as nearly as possible, 

 I will adopt these two genera, commencing with the 

 genus .l/ii.v. 



Ata.t has been also divided into two groups, free- 

 swimming and parasitic. The parasitic are to be 

 found within the shells of the fresh-water mussels. 



Piersig describes from Germany seven species in 

 the genus Atax. In Britain we are behind this 

 number, but I hope our list will be later increased. 



The chief characters of this genus are : Body 

 soft. The first pair of legs of an unusual thickness. 



In the free-swimming species the first pair of legs are 

 provided with long, stout, movable, sword-shaped 

 spines. Second pair of legs usually longer than the 

 third pair. Epiniera in four groups, the posterior 

 pair being large and having rectangidar claws to all 

 feet. Eyes wide apart. 



Fig. I. Atax crassi/ts. Ventral surface of ftm.-ilc, showing 

 papillae on posterior margin. 



I. Ata-x crassipcs 'MxiWer. 



Fk.mai.e Body oval in fonn. length about 



1.20 mm. Colour a pale transparent yello%v, with 

 brown markings on the dorsal surface, and a brighter 



