6o 



SCIENCE-GOSSIP. 



aperture oblique, transverse lunate, margins 

 approaching ; peristome straight, simple, acute.] 



Pyramidula perspectiva appears to be the nearest 

 ally of this species, but the latter differs in having 

 much closer and less coarse ribs, a more flattened 

 spire, and a less impressed suture. 



The specimen here figured (fig. 8) was 

 obtained from Bruch, near Barcelona, through 

 Mr. J. E. Cooper, of Highgate ; its dimensions 

 are: diam., maj. 7'25, min. 6-5, alt. 2-75 mm. 



Westerlund (" Fauna der in der Palaarctischen 

 Region lebenden Binnenconchylien " i., p. n.) 

 gives as habitat : France — Basses-Pyrenees and 

 Dordogne; Spain — Montserrat. 



Mr. Pilsbry, in "Manual of Conchology," ix. 

 (1S95), p. 341, has altered the name to Pyramidula 

 omalisiana, stating the name omalisma to be a 

 printer's error, but on referring to the original 

 description, I find the name as cited above. 

 5, Gicibach Road, London, N. ; July 24th, 1896. 



COMMENSALISM OF DAPHNIA AND ROTIFERS. 



By Major-Gexer.a.l Warraxd, R.E. 



/^N June 2Sth I was out shepherding on my 

 ^■^^ farm in Nottinghamshire (a loamy clay soil 

 in the Keuper or new red sandstone) when I saw 

 on a small pond in a grass field a number of red 

 patches, apparently of the blood of some animal. 

 The red patches varied in size from half a square 

 foot to four or five square feet. I thought that 

 some animal must have had an accident, and asked 

 the shepherd if any cow or sheep was missing, 

 but it turned out that every animal of my herd was 

 safe and in good health. It struck me that the red 

 patches must be due to some algse, and the next 

 morning my man brought me a small bottle of the 

 water, which I found to be one mass of DapJmia 

 pulex, to which clung an innumerable host of 

 rotifers very like Pomphobyx sulcata (fig. 2, plate 

 xxvii., of Hudson and Gosse). 



Mr. Baird (page 78 of " British Entomostraca ") 

 says: "On a sunshiny day, in a large pond, a 

 streak of red, a foot broad and ten or twelve yards 

 in length, will suddenly appear in a particular 

 spot, and this belt may be seen rapidly changing 

 its position, and in a very short time wheel 

 completely round the pond. Should the mass 

 come near enough to the edge to allow the 

 shadow of the observer to fall upon them, or 

 should a dark cloud suddenly obscure the 

 sun, the whole body immediately disappears, 

 rising to the surface again when they have reached 

 beyond the shadow, or as soon as the cloud has 

 passed over." 



In my pond, however, which was only about 

 twelve yards long and six yards wide, the red host 

 took no notice of the shadow, or of a bottle being 

 thrown in their midst to catch them ; they were 

 of all sizes, and packed together in an extra- 

 ordinary manner, and remained in this packed 

 state for at least three daj's. 



The rotifers and daphnia evidently dwell 

 together in the partnership know^n as " Com- 

 mensalism " see Science-Gossip, vol. iii., p. 5), 



the former get conveyed from place to place 

 without any exertion of their own, and conse- 

 quently find an advantage in attaching themselves 

 to the daphnia ; but often a daphnia gets over- 

 burdened by its friends, who sometimes, to the 

 number of at least a dozen, will take the oppor- 

 tunity of providing themselves with an easy mode 

 of locomotion by attaching their tails to various 

 parts of the body of their host. When the daphnia 

 were placed in a watch-glass several of them died, 

 but their attendant rotifers at once attached 

 themselves to the sur\dvors, and, as above stated, 

 an unfortunate daphnia might be seen together 

 with at least a dozen Pomphobyx. 



I was asked a short time since to send some 

 rotifers from this neighbourhood, by post, to a 

 friend in the south of England who is clever at 

 mounting and preserving them by Mr. Rousselet's 

 process. He warned me not to send Entomos- 

 tracse in the same tube as the rotifers, as the 

 latter would get eaten by the former on their 

 journey. So I suppose that it is well known 

 that rotifers form to some extent an article of 

 food for the water-fleas, and instead of being a 

 case of commensalism, this, I think, may account 

 for the daphnia congregating in patches, in order 

 that each creature may destroy the tormentors of 

 its neighbours. In the same way horses collect 

 together when attacked by the gadfly and defend 

 each other from the attacks of their small per- 

 secutors, by biting and rubbing each others backs, 

 preventing the flies from settling, thus forming a 

 sort of " mutual accommodation society." 



Perhaps some of 3'our scientific readers will be 

 able to give a better explanation as to why the 

 Entomostracas should pack themselves together in 

 the manner above stated. It was evidently not 

 caused by a desire for sunning themselves, as 

 stated by Mr. Baird, for they remained in much 

 the same places for at least three days. 

 Westhorpe, Southwell, Notts; July 10th, 1896. 



