101 



HARDWICKE'S SCIENCE-GOSSIP. 



MICROSCOPY. 



Melicerta ringens. — In an article on "Ro- 

 tifers" (S.-G., p. 110), your contributor "E. S.," 

 speaking of the Melicerta ringens, says : "It is not 

 easy to trace the process of receiving, smashing up, 

 manufacturing, and placing the pellets, from 

 beginning to end. So far as I could form an opinion, 

 it seemed to me that the particles received through 

 the mouth passed at once to the gizzard to be 

 smashed up, and were thence conveyed to an organ 

 called, I believe, by Mr. Gosse, from its function, 

 the 'mill,' and from its shape, the ' ventilator, 5 to 

 be formed, by rapid rotation and mixing with some 

 viscid fluid, into balls." This view of the subject 

 appears to me entirely to differ from that of Mr. 

 Gosse and other observers of this interesting rotifer. 

 Mr. Gosse states clearly that the particles which 

 pass to the gizzard, and thence into the stomach, 

 are quite distinct from those which are carried by 

 ciliary currents into the "mill," or brickmaking 

 organ. He says that the latter particles " swiftly 

 glide along the facial surface, following the irregu- 

 larities of outline with beautiful precision, dash 

 round the projecting chin like a fleet of boats 

 doubling a bold headland, and lodge themselves, 

 one after another, in the little cup-like receptacle 

 beneath. The action of the cilia which perform 

 this transport is clearly seen, and I believe that 

 they are continuous from the great sinus to the 

 cup." Eurther on he says, " Some atoms of 

 iioating carmine now and then passed down the 

 oesophagus into the gizzard, and thence into the 

 stomach ; but these were quite independent of, and 

 unconnected with, the pellets, which were composed 

 exclusively out of the torreut that had passed by 

 the disk."— Trans. Mie. Soc, 1851, vol. iii. part ii. 

 page 62. My own observations quite agree with 

 Mr. Gosse's views ; by mixing carmine with the 

 water, and viewing the object, say with a power of 

 120, and dark ground illumination, the course of the 

 particles can be plainly seen. I may mention that I 

 obtained Melicerta in considerable quantity on the 

 occasion of the South London excursion to Barnes 

 Common, on April 15th. They were attached in 

 large numbers to the submerged leaves of the 

 water ranunculus. By placing them in a small 

 aquarium, 1 have succeeded in keeping them alive 

 up to this date (May 15th), and also in obtaining a 

 number of young Melicerta, hatched since the weed 

 was placed in the aquarium. One great disadvan- 

 tage of "E. S.'s" plan of observing these rotifers 

 (by placing them on a glass slide, covered with a 

 thin circle) appears to me to be that it is difficult to 

 keep the Melicerta alive for any length of time. It 

 is often interesting to keep one individual under 

 observation for some days, and frequent change of 

 water is then absolutely essential. I have found 

 it an excellent plau to place the Melicerta in a 



small zoophyte trough, about T V inch thick. The 

 rotifer can then be readily examined with powers 

 up to 250 (| inch C), and when done with, the 

 slide can be suspended by a piece of wire in the 

 aquarium from which the Melicerta was taken, and 

 there left until again required for observation. This 

 plan I have found to answer capitally, the Melicerta 

 when taken out almost invariably having their lobes 

 extended, and the cilia in full play. — T. G. A. 



Scales of the Gbayling {Thymallus vul- 

 garis). — The scale figured below is that of another 

 of the British fishes, in continuation of our series. 

 By comparison with the figures already given, it 



Fig. 36. Scale of Grayling:. 



will be seen that variety is not exhausted, and we 

 have here a very characteristic scale, sufficiently 

 different from all the rest to secure for it a place in 

 every good cabinet of objects. 



Pollen for the Microscope. — Beferring to 

 the recommendation for mounting (Science-Gossip, 

 June, 1871) of the pollen of composite and mal- 

 vaceous plants, I can say that the muricated pollen- 

 grains and the scares for the pollen-tubes in these 

 plants are often very beautiful. But to get a 

 knowledge of the value of the character afforded by 

 the pollen in the diagnoses of plants, our observa- 

 tions should be greatly extended ; and they are well 

 calculated to afford many an agreeable and instruc- 

 tive hour with the microscope, particularly to ladies. 

 Even nearly allied plants may, in several genera, 

 be known by their pollen-grains. Thus, in the 

 "Popular Science Review," July, 1SGS, and in 

 Seemann's " Journal of Botany," Sept. 1S66, Pro- 

 fessor Gulliver has shown, amoug other examples, 

 that the Ranunculus arvensis is readily distinguished 

 by its large and rough pollen-grains from Ranunculus 

 hirsutus. Such observations should be multiplied, 

 and would afford an elegant microscopic pursuit for 

 ladies, who might thus increase our knowledge of 

 good though minute characters for systematic 

 botany— G. G. 



