46 



SCIENCE-GOSSIP. 



maleiial, and sometimes the \ety delicate red and ijlue 

 colour of the dorsal shield can be seen. If the dorsal 

 plate be dissected from the dead mite, cleaned and 

 mounted in Canada Ijalsam, it makes a very beautiful 

 object for the microscope, the finely granulated 

 texture with the delicate colouring of transparent red 



Mideo/isrs oi-biculat-is Muller. 



and blue, reminding one of those circular diatoms, 

 which from their thinness, decompose the light. 



Legs. — These are pretty equal in thickness, and 

 length ; all of them are provided with claws, and 

 swimming hairs, which are more numerous on the 

 three last pairs. 



Palpi. — The palpi are short, and pretty stout, the 

 last joint is claw-shaped, not simple, but does not 

 make a forceps, as in the Arrenuri. The thigh plates 

 are of a delicate blue colour, and coalesce, so as to 

 form a sort of shield, over the central portion of the 

 abdomen ; and a well-marked sort of bay is formed 

 posteriorly, between Ihem, by their projection on 

 either side. The skin is chitinous, and very finely 

 perforated, tougher and not so brittle as in Arrenurns. 

 The thigh plates are more highly chitinized than the 

 skin, the perforations are larger, their colour is inten- 

 sified by mounting in balsam. 



Genital Plates. — In the centre of the bay, 

 formed by the two posterior thigh plates, are the 

 "two remarkable genital plates; each plate having three 

 genital discs on the outer side, placed in a line, the 

 one behind the other ; as is well seen in Mr. Soar's 

 accompanying characteristic figure. 



The Male differs very little from the female. It 

 is somewhat smaller, and a little nipple-like projection, 

 in the centre of the posterior edge of the body, is 

 usually conspicuous. 



The Larva is ver)- small, and circular. I have 

 not been able to make out, whether the larva is 

 parasitic ; and if so, I have no idea what creature 

 forms the host. 



The Nymi'H, though larger than the larva, is 

 small in comparison with the adult; and has t\v« 

 genital discs on each side. 



Localities. — This mite is not rare, though I have 

 not found it very abundant. It occurs with Arrenuri 

 and is easily identified by its circular figure, and 

 rather slow movements when crawling on the sides of 

 the vessel in captivity. 



I do not know of any other species of this genus. 



Piersig gives very beautiful figures of the larva and 

 nymph, but more highly coloured than the specimens 

 with which I have met. I first figured this interesting 

 freshwater mite in my note book in May, iSSi. 



Kirton hi Lindsey^ 



Lincolnshire, May, iSg<^. 



DOUBLE CANALS IN MARS. 



IV/r R. FRANK DENNETT, writing in )Our 

 ■^ •'■ Astronomical Columns (Vol. v., page 2S3), 

 attributes the peculiar phenomenon of the visibility of 

 double canals in Mars to the imperfect focussing of 

 the telescope. This appearance has been the subject 

 of a good deal of controversy since the time of its so- 

 called discovery bj' Schiaparelli, with his 83 inch 

 telescope at Milan in 1S77. That this double 

 appearance of canals is not due to imperfect focussing 

 of the telescope, as stated by Mr. Dennett, can be 

 determined by the fact that almost all observers of 

 the planet Mars have noted this phenomenon, and if 

 it were really caused by bad focussing, the canals on 

 the entire disc would appear double at one and the 

 same time ; whereas certain canals have appeared 

 double and others single in one night, and on 

 another night this order of things has been reversed. 

 As one of the causes, for it is my object to point out 

 several, for this appearance, I must mention that the 

 rotation of the planet on the one hand and that of 

 the Earth on the other, must be taken into con- 

 sideration. Further, it is 2, well-known coincidence 

 that persons affected with astigmatism, always see 

 objects duplicated with the defective eye when view- 

 ing objects from a certain angle, and it might also be 

 partly to this condition that Martian gemination is 

 attributable. The planet is closely surrounded by 

 clouds and vapours and this marvellous duplication 

 may also result from the amount of refractive aberra- 

 tion due to the surrounding density of the atmosphere. 

 One important fact connected with this duplication, 

 and why all the canals are not seen double at one and 

 the same time, should be sought for in the presence of 

 a direction in which the geminating phenomena 

 attain their maximum intensity, at right angles to 

 which there is no doubling. Antoniadi attributes it 

 chiefly to a temporary inability of the eye to define 

 linear markings well nigh at the limit of visibility, 

 and does not wholly put it down to astigmatism. 

 That the density of the atmosphere in places of 

 observation of comparatively low altitudes is 

 undoubtedly one of the causes of this duplication, is 

 patent from the fact that the planet when viewed 

 through the great Lick telescope in the pure 



