HARDWICKE'S SCIENCE-GOSSIP. 



211 



knife draw the head from the body, the head brings 

 with it the stomach, gizzard and chief portion of 

 digestive organs. Eyes, after being cut from the head, 

 are soaked for a short time in liquor potass ; they 

 may be mounted dry, the facets show well ; or soak 

 in equal parts of gly. spirit and water, and mount in 

 gly. jelly. Tongue mount as above. Spiracles 

 soak and mount as above, but to see them properly, 

 the skin must be stretched to show the part between 

 the segments. The salivary glands sent to P. M. Soc. 

 boxes by Mr. A. W. Lyons were stained carmine and 

 mounted in C. b. and benzole.— V. A. Latham. 



ZOOLOGY. 



The Air-Bladder of Fishes.— A very interesting 

 paper on this subject by Mr. Charles Morris is printed 

 in the " Proceedings of the Academy of Natural 

 Sciences of Philadelphia." He describes the air- 

 bladder as at present most generally a closed sac, 

 containing, in fresh- water fishes, nearly pure nitrogen ; 

 in ocean fishes, particularly in deep swimmers, a' 

 sometimes considerable excess of oxygen. He con- 

 siders that the air-bladder is not now an organ of 

 functional importance, though it may serve certain 

 uses, such as to raise or lower the fish in the water, 

 to keep its back uppermost, to raise or depress the 

 fore part of the body, &c. He looks upon it as a 

 survival of a breathing organ, and as being now on 

 the road to extinction. This view he supports by 

 reference to embryological evidence and to the con- 

 dition of existing ganoids and elasmobranchs, as 

 affording indications of the possible state of matters 

 during the Silurian and Devonian period when these 

 two orders were abundant. Existing elasmobranchs 

 are destitute of air bladders, both in the larval and 

 mature stages ; while existing ganoids possess one 

 which retains a fully-developed pneumatic duct in the 

 mature stage. The sub-order of the Dipnoi possesses 

 a bladder functionally active as a lung. Of these 

 latter the Australian lung-fish (Ceratodus) has a 

 single air-bladder with symmetrically arranged 

 breathing pouches, and is supposed to breathe with 

 its lungs when the water is muddy or otherwise unfit 

 for use. Finally Lepidosiren and Protopterus have 

 completely formed lungs of cellular structure with 

 two lateral chambers and a pulmonary artery. Mr. 

 Morris thinks that not only may the ancient fishes 

 have used their air-bladders for the occasional direct 

 breathing of air when the water was thick or muddy 

 or lacking in sufficient aeration, or when the pools 

 dried up, though it was such causes as these that 

 probably led to the original development of the air- 

 breathing organ, but that in the absence of foes in the 

 shape of vertebrate land animals they may have 

 gained the habit of leaving the water temporarily in 

 search of food. Since even now, when so many 



active enemies are to be found in the land, many fish 

 do invade the shore, and some even climb trees, he is 

 of opinion that it is quite possible that in the early 

 period when it could be done without danger, very 

 many fishes may have paid temporary visits to the 

 land. 



LlMN/EA Stagnalis a Paper-feeder.— This 

 afternoon I visited the pond on Chislehurst Common, 

 where the variety of L. stagnalis which I provisionally 

 call elega?itula abounds. The hot weather had much 

 diminished the size of the little pond, and the water- 

 weed {Potamogeton crispus) is quite insufficient 

 apparently to supply the wants of the very numerous 

 Limnasae as well as an abundance of Planorbis spirorbis : 

 At one particular spot, however, there seemed to be 

 something very enticing, for here the L. stagnalis 

 were gathered together, so that for the space of about 

 a square foot nothing else could be seen. Being 

 curious to ascertain the reason of this vast assembly, 

 I divided the crowd. The attraction was nothing 

 more than an old newspaper, which had probably 

 been blown into the pond, and which was torn to 

 shreds and partly devoured by the ravenous snails. 

 It did not contain anything wrapped in it, the paper 

 was the sole attraction. Helices in confinement, as 

 most collectors are aware, will readily eat paper if 

 they can get nothing better, but I never heard of 

 Limnsea doing so before. I brought some of these 

 snails home and put them into some water with 

 paper, pelargonium and rose petals, leaves of ivy and 

 bracken, and flowers of Vicia cracca. They " went 

 for " the pelargonium petals, and these are already 

 riddled with holes.— 71 D. A. Cockerell. 



The Nest of the Fifteen-Spined Stickle- 

 back.— Professor Karl Mobius says that the sea- 

 stickleback (SpiuacAia vulgaris, Flem.) constructs a 

 nest for its eggs and young, employing delicate 

 shallow water plants, making with these a soft 

 rounded mass 5-8 centim. in diameter upon Zosters, 

 seaweed fronds, or piles of landing-stages, which 

 nest the male surrounds with white silky threads, and 

 then keeps watch over. Professor Mobius has been 

 able to throw light upon the previously unknown 

 origin of these white threads. He says they are 

 nitrogenous, made of a peculiar modification of 

 mucine, and are formed in the kidney of the male, 

 which produce it during the breeding-season only ; and 

 the male fish has only to swim round the nest while 

 the thread-forming mucus is given off, and this 

 attaches itself to solid objects that it touches. Further 

 details may be found in a translation given in the 

 August number of the "Annals and Magazine of 

 Natural History." 



Mollusca in Manitoba.— In the "Journal of 

 Conchology " for July may be found a paper by Mr. 

 Robert Miller Christy, entitled "Notes on the Land 

 and Freshwater Mollusca of Manitoba." The writer 



