ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 311 



lithium, bromine, iodine, &c, may cause rhythmical contractions in 

 muscle, while other solutions with other ions of calcium, potassium, 

 magnesium, barium, strontium, &c, check such contractions. It is 

 supposed that the rhythmic contractions are the result of the combina- 

 tion of the favourable ions with the muscle. This should be collated 

 with Loeb's research, already recorded, on the artificial production of 

 parthenogenesis in the ova of sea-urchins. 



Specific Gravity of Animals.* — Mr. S. R. Williams has determined 

 the specific gravity of certain fresh- water animals, and finds that it variei 

 from 1*0095 (Hydra viridis) to a maximum of 1'046 in Gypridopsis. The 

 movements of an animal are closely related to its density, and there is 

 also a correlation between density and food habits. Of the animals 

 tested, Stentor represents a typical case of but slightly modified proto- 

 plasm ; the heavier animals have some specialised tissues which are 

 denser ; in Hydra (the lightest) the extreme vacuolation of the inner 

 layer is well known. In the case of the developing animal, the chief 

 tissue to absorb water, and therefore the tissue of most rapid increase 

 in bulk, is the mesenchyme. All the walls of the internal organs, how- 

 ever, grow thinner and less dense as the animal increases in size. 



Diastatic Ferment in Hen's Egg.f — Herr J. Miiller has discovered 

 that the yolk of a newly-laid hen's egg exerts a distinct diastatic influence. 

 The optimum temperature for the action of the ferment is 37° C. ; free 

 acids and alkalies, even in slight concentration, inhibit the action. 



Mimicry in Snakes. ! — Prof. 0. Boettger, in the course of a general 

 lecture on snakes, discusses in some detail instances of mimicry by harm- 

 less snakes of poisonous species. Thus a collection of snakes from Brazil 

 showed that the prevailing colours are red, black, and white or yellow, 

 arranged in certain definite patterns. The coral snake (Elaps) is the 

 only genus which is markedly poisonous, and all its species display these 

 vivid contrasting colours. Eight other snakes, belonging to as many dif- 

 ferent genera, display the same tints ; and as, with the doubtful exception 

 of two, they are all innocuous, the colours must be regarded as mimetic. 

 In Mexico species of Elaps also occur, and are mimicked there by species 

 of Geophis, Tropidodipsas, Coronella, &c. In tropical India the poisonous 

 snakes Doliophis, Callophis, and Hemibungarus are mimicked by Cala- 

 maria, Polydontophis, and Ablabes. As in these cases the poisonous 

 forms prey upon the mimics, the colouring must only protect the latter 

 from other foes, such as birds and lizards. The suggestion of mimicry 

 between Callophis aud Doliophis made by A. B. Meyer is rendered im- 

 probable by the fact that both are poisonous. The sea-snakes Hydrophis 

 and Distira are mimicked by Hipistes hydriims and Chersydrus granulatus 

 which live in brackish water. In Africa the egg-eating snake Dasypellis 

 mimics the poisonous Edits. 



Reappearance of the Tilefish.§ — Prof. H. C. Bumpus notes that 

 during the summer of 1898 the investigations of the U.S. Fish Com- 

 mission brought to light the fact that the tilefish (Lopholatilus chamse- 

 leonticeps), once supposed to be extinct, now occurs in great numbers off 



* Amer. Nat., xxxiv. (1900) pp. 95-108 (3 figs.). 



t SB. Phys.-Med. Ges. Wiirzburg, 1899, pp. 95-6. 



t Ber. Senckenberg. Naturf. Ges., 1899, pp. 75-S8 (7 figs.). 



§ Bull. U.S. Fish Commission, 1898 (published 1899), pp. 321-33. 



