454 



NATURE 



\March n, 1880 



Ural Crayfish. — Part 2, vol. v. of the Bulletin de la SocietJ 

 Ouralienne a' Amateurs des Sciences naturellcs & Ekatherincbourg 

 contains a very interesting memoir on the crayfish of the rivers of 

 the Middle and Southern Ural, by M. Malakhoff. Prof. Kesslerin 

 his fine work in the memoirs of the Russian Society of Entomology, 

 "On the Crayfish of the Rivers of Russia" points out that the data 

 about the life of the fluviatile crayfish are still very incomplete, 

 and in part even contradictory, anddeclares that it is very desirable 

 that new researches should fill up the one and dissipate the 

 other. Among the queries he starts is one as to how far the 

 crayfish have spread into the rivers of Western Siberia ? in which 

 of its rivers is it to be found ? and is it true that those found are 

 insipid as food ? In this memoir, M. Malakhoff does his best to 

 answer these, partly from personal observations, partly from 

 those who had lived long in those parts of the country, such as 

 fishermen, and partly from indications scattered through different 

 works. He writes of the geographical distribution of the cray- 

 fish in the Middle and Southern Urals ; giving a brief historical 

 account of their successive propagation in the rivers of the 

 watershed east of the Ural Mountains belonging to the basin of 

 Western Siberia. Among the references here given, is one to a 

 work, apparently not yet published, by J. S. Poliakoff entitled 

 "Letters and Notices of a Journey in the Valley of the Obi." 

 The species peculiar to this district would seem to be Astacus 

 leptodacty/us, Esch. ; its northern limit would appear to be con- 

 siderably to the north of the Ural ; in the western region of the 

 Ural it is found in many of the rivers and in considerable 

 numbers : a detailed list of these is given. To the south it is 

 found in the River Ural and most of its affluents. Facts 

 seem to prove that the species is not indigenous to the eastern 

 watershed of the Ural, nor in Northern Siberia. It would 

 appear, however, under fitting circumstances to be very easily 

 brought into cultivation. In the Middle and Western Ural it is 

 to be met with from 100 to 175 mm. in length. A mountain 

 variety possesses a cephalo-thorax, strongly serrated on the sides 

 and angles ; another, living in the River Ural, is remarkable for 

 little asperities crowded together, which cover over the cephalo- 

 thorax and chelae. In the Ural the natives call the freshwater Unio 

 Rak (Ecrcvissc) and the true crayfish Rak-ryba (I Ecrevisse poisson). 

 Prof. Kessler's opinion as to their insipidity is declared to be 

 wrong, as in general the crayfish are of excellent quality. In some 

 districts they increase so much as fully to come up to the fisher- 

 man's description of "swarming ; " in some rivers, owing to their 

 number, they interfere with the capture of fish ; not only will the 

 nets be found filled with them, but what fish may be taken in these 

 will be found spoiled and many are eaten. They will sometimes 

 cross a good stretch of dry ground to get to a river with good 

 feeding, though that this is a fact is denied by many. Ths 

 people use the stones found in the crayfish stomachs as a remedy 

 against struma. The distribution of Mustela lutreola in the 

 Ural mountains seems to be dependent on the distribution 

 of this crayfish, which would seem to be its principal food. — It 

 ought to be mentioned that the memoirs of this Society are 

 published in the original Russian, with a French translation in 

 alternate columns. 



Development of "Amblystoma punctatum." — Early in 

 March of 1S78 Dr. Samuel Clarke, of the Johns Hopkins Uni- 

 versity, obtained a mass of the eggs of the above batrachian. 

 They were found clinging, in gelatinous, variously-sized masses, 

 to aquatic plants, the masses containing from 4 to 200 eggs, and 

 were partly composed of a milky, gelatinous matrix. Each egg 

 is surrounded by two membranous shells, and the large space 

 between these two is filled with a clear fluid. The eggs being 

 laid by the female, the males, so far as the observations made 

 on the animals in confinement went, then strewed the sperm- 

 masses in the vicinity of, but not on, the ova, and not immediately 

 on these latter being laid. Shortly afterwards, however, the eggs 

 were found to be covered over with actively-moving spermatozoa, 

 and though the e were never actually found within even the 

 outer shell of the eggs, yet most of those which were laid during 

 the night were found by nine o'clock the next morning to show 

 the first segmentation-burrows. In Dr. Clarke's paper on the 

 development of these eggs, very minute details are given as to 

 the results of segmentation, which are illustrated by numerous 

 figures. The following is his own resume': — after segmentation 

 an area made up of large cells appears around the lower pole of 

 the egg, which, at first hemispherical, then oval, and finally 

 circular, forms the vitelline plug of Ecker. This plug protrudes 

 from the egg, then sinks into it, while from the diminishing area 

 around the di- appearing plug stretches away the anal portions of 



the medullary folds with the medullary groove midway between 

 them. The two folds grow forwards and unite near the opposite 

 pole. The medullary folds close in and unite, forming the 

 neural tube. The body elongates, is covered with cilia, and 

 rotates horizontally upon its axis. The head is marked off, and 

 the optic vesicles appear. The branchial lobes and the lobes of the 

 cephalic balancers appear, soon followed by those of the anterior 

 limbs. The pericardial region is marked off, and the pulsations 

 of the heart are visible. The nasal pits and the position of the 

 mouth are indicated. The tail and the dorsal fin grow rapidly, 

 and the branchial lobes are divided into three pairs of branchiae; 

 these give off processes. The eyes develop rapidly, and the 

 mouth is moving forward. A constriction takes place across 

 the ventral surface of the neck, and balancers, now fully deve- 

 loped become capitate. The branchiae still further develop ; 

 the balancers become more and more slender as the anterior 

 limbs increase in length, and the blood ceasing to circulate in 

 them, they drop off. The anterior limbs now develop rapidly; 

 first, the first and second digits, then the third, and finally 

 the fourth. The first two digits on the posterior limbs are 

 formed on the fourth digits on the anterior limbs, one budding- 

 out, then the third, fourth, and fifth in succession. Up to 

 about the sixtieth day the external parts are being gradually 

 formed ; by this date it reaches a stage, after which it undergoes 

 no further external change beyond a general growth, until the 

 branchiae begin to decrease in size as they are being absorbed. 

 This change took place in reared specimens in about one 

 hundred days from the commencement of segmentation. The 

 process of resorption of the branchirc begins at their distal 

 ends ; the outer processes become shorter and disappear, until 

 nothing is left but three pairs of small rounded processes, which 

 are very slowly indeed absorbed. The whole of this process 

 lasts from three to five days ; they then become air-breathers, 

 and take up their abode in damp localities on the land. Some 

 specimens developed much more slowly ; one, hatched about the 

 middle of May, retained its branchix until the end of the fol- 

 lowing October. In confinement the tadpoles were hard to 

 keep supplied with food. When hard up they would bite each 

 other's gills off, and then begin to eat the tips of each other's 

 tails ; and even when big enough they would swallow up bodily 

 their smaller brethren. Although endowed with an immense 

 power of reproduction of lost parts, it seems remarkable that, 

 once a portion of a branchial tuft was bitten off, it never, at 

 least in hundreds of cases tried, became reproduced. In 

 a second memoir the author promises to treat in detail of 

 the changes that take place in the development of the internal 

 rarts. 



Stimuli in Sensitive Nerves. — In experiments on the 

 rate of propagation of stimuli in sensitive nerves it has been 

 generally assumed that, under like conditions of experiment, 

 and with an equal length of nerve-path from the point of 

 stimulation to the centre, the reaction time is always the same. 

 This, tested recently by Messrs. Hall and Kries (Du Bois- 

 Reymond's Arckiv, 1879, Supplement, p. i), is found to be 

 not confirmed. Stimulating with a slight induction shock the 

 finger point and the middle of the outer side of the upper arm, 

 the reaction in the latter case occurred with Mr. Hall later than 

 that from the finger (on an average about 0005 second). In 

 Herr von Kries, the reaction time was shorter (about 0003 sec.) 

 from the upper arm than from the finger. Again, the reaction 

 time was measured when light was made to strike different 

 parts of the retina and even here (the lengths of nerve- path beirg 

 equal) presented considerable differences. In Mr. Hall's case 

 the difference between the outer and inner part of the retina was 

 o - oi8 sec, that between the upper and lower O'oaS sec. ; in 

 Herr von Kries's the differences were respectively 0"o6i and 

 o 064 sec. In comparison with the place of direct vision still 

 greater differences appeared. Experiments were also made in 

 stimulating the forehead and the tongue, in which cases the paths 

 were assumed to be nearly equal. In both observers the reaction- 

 time from the tongue was somewhat longer than from the fore- 

 head, though, according to Weber, the sense of space at the tip 

 of the tongue is about twenty times finer than on the forehead. 

 The authors conclude that the reduced reaction times differ 

 considerably according to the place of stimulation, that in 

 the eye the differences are connected with differences of 

 functional power, that the reaction method is not available 

 for ascertaining the velocity of conduction in sensitive and 

 motor nerves, and therefore the velocity in the spinal cord is 

 still unknown. 



