HARDWICKE'S SCIENCE-GOSSIP. 



107 



tlie microscope, movements may be observed when 

 these cells are stimulated by light ; the pigment 

 granules at one time congregating in a spheroidal 

 mass round the nucleus, at other times becoming 

 diftused in a radiating manner through the cells or 

 into the processes. 



I began these experiments under the impression 

 that the peculiarities of structure presented by the 

 ova and tadpoles had reference to the heat rays of 

 the sun. A ray of light is a very complex object, and 

 is resolved by a prism into three primary constituents, 

 the luminous rays, the heat rays, and the chemical 

 rays. The luminous rays produce the familiar coloured 

 band termed a spectrum : the chemical rays and the 

 heat rays are invisible. It is the chemical rays which 

 act as stimuli to the healthy development of the ova 

 and tadpoles. Professor Jung, of Geneva, has lately 

 been experimenting on the effects of coloured light 

 on the eggs of frogs and fishes, and has shown that 

 their development is quickened by those colours which 

 are situated at the chemical end of the spectrum. 

 Precisely the same effects have been observed in 

 plants. The chlorophyll, or colouring matter of 

 plants, is analogous to the pigment of animals. Pring- 

 heim showed the action of the sun's rays on chloro- 

 phyll by experiments similar to those of Jung. That 

 the effects produced were in no way due to the heat 

 of the sun's rays was .shown by interposing in the 

 path of the beam various coloured media, when it 

 was found that a blue solution, which shuts off 

 nearly the whole of the heat rays, had no effect in 

 stopping the action of sunlight ; while with a red 

 solution, allowing eighty per cent, of the heat rays to 

 pass, the cell and its chlorophyll contents remained 

 quite unaltered. The representation of images on 

 the retina is now known to be photo-chemical. More- 

 over, Professor Tyndall performed a remarkable 

 experiment to show that the heat rays had no action 

 upon the eye. Excluding the luminous rays by means 

 of a layer of iodine, he brought the heat rays to a 

 focus on the retina, but no impression of light was 

 produced The optic nerve was not even conscious 

 of heat, although a sheet of platinum placed in the 

 same position became red hot. 



We have thus both positive and negative proof that 

 it is the chemical rays of the sun which act on the 

 ova and the tadpoles. 



Allow me now briefly to recapitulate the principal 

 facts which these experiments demonstrate, viz. : — 



That the ova and tadpoles of the frog possess a 

 structure specially adapted for the reception of the 

 sun's rays. 



That the stimulus of the sun's rays is necessary to 

 enable them to arrive at maturity, although develop- 

 ment will proceed to a certain stage in the dark if 

 moderate warmth be supplied. 



That the chemical rays of the sun are the chief 

 stimulating power. 



That this chemical stimulus must be necessary 



from the period when development begins, is shown 

 by the hatching of weakly tadpoles when the light is 

 withdrawn, and by the acceleration of development 

 under blue light. I am inclined to believe that it is 

 also to a great extent for protection that pigment is 

 present in the ecto-sac of the ovum, to prevent the 

 delicate structures beneath from being destroyed by 

 the heat of the sun's rays. The humours of the eye 

 are known to be highly impervious to the invisible 

 calorific rays. The gelatinous matter has doubtless 

 the power of absorbing a large proportion of the rays 

 of light which fall on its surface. All other animals 

 which lay eggs with clear gelatinous envelopes — e.g., 

 newts and snails — deposit them in sheltered places, 

 such as the under-surface of the leaves of aquatic 

 plants, where they cannot be injured by sunlight. 

 But the ova of the frog are deposited in exposed 

 situations by the side of ponds and ditches, and 

 nature makes provision for their protection by covering 

 them with a thick layer of pigment. 

 Stoke-on-Trent. 



OBSERVATIONS ON CROWN ANIMALCULE 

 {STEPHANOCEROS EICHORNII). 



DURING the month of November of last 

 year, myself and my fellow microscopist, 

 Mr. Dean, whilst searching a pond in this neigh- 

 bourhood, alighted on a colony of Stephanoceros 

 EicJiornii ; this we thought was remarkable, owing 

 to the lateness of the season, and more so because 

 I had groped this pond all the summer without 

 success. They were grand specimens, exceedingly 

 healthy, and the ovary was full of ova, and afforded 

 a good opportunity of watching and making a few 

 observations on the incubation of the ovum of this 

 beautiful creature. I was unfortunate in not seeing 

 the ovum escape from the ovary, but on December 3rd, 

 I discovered the egg in a receptacle of the cell close 

 to the mouth, as seen in fig. 76, a. What struck me 

 as very remarkable about the ovum was the fact that, 

 instead of sinking down the cell and consequently 

 under the creature, as is the case with the eggs of the 

 Floscularise, it came to the surface, and was received 

 in a recess of the cell. It was also remarkable that 

 as the parent receded into its cell, either from sound 

 or gulping its food, the ovum is dragged partially down 

 the cell and left in that position, and on the return 

 of the creature is forced upwards into its receptacle. 

 Whether there is an attachment, in the shape of 

 ligatures from the parent to the ova, I am not able 

 to discover, but I am led to infer that there is, because 

 in descending the ovum is dragged down by its pos- 

 terior end (fig. 76, b) and rises again as the creature 

 emerges out of its cell. I am very much inclined to 

 believe the theory of there being a ligature, because 

 as the creature approaches maturity the ovum did not 

 recede with the parent into its cell, but remained in 



