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HARDWICKE'S SCIENCE-GOSSIP. 



Pond Life.— Mr. E. W. Wilton, of Northfield 

 Villas, Leeds, has appointed a large number of 

 professional collectors in various parts of Great 

 Britain and other countries, so as to supply students 

 with living objects. This will be a great boon to 

 the increasing number of microscopists who find little 

 time or opportunity to collect for themselves. 



Microscopical Drawings. — I have read with 

 much interest, the notes on drawing from micro, in 

 your columns. Most people imagine that such drawings 

 can only be made with the aid of an expensive 

 camera lucida, and little dream that one of the thin 

 glass covers of which they have such numbers, will, 

 when properly adjusted to the eye-piece, produce 

 an exact image of any transparent object placed on 

 the stage. All that is needed is a small thin piece of 

 brass or tin to hold it and clip the eye-piece, so 

 that the bottom of the cover corresponds with the 

 bottom of the lens. The light will require some 

 adjusting, and if there is failure, it is due to the light 

 not being properly adjusted. I find that the light 

 should be some distance from the table, at right 

 singles to the microscope, so as to throw the same 

 amount on the drawing as on the mirror. For those 

 who do not care for the trouble of making such an 

 elaborate apparatus, Mr. Bolton, of Birmingham, 

 supphes them post-free for eightpence ! if applied for 

 by the name of " Finest reflectors."— y«7/^;^ Alcxajidcr 

 Ollard. 



Mr. Thomas Bolton's " Portfolio."— No 7 of 

 this periodical issue of drawings and descriptions of 

 living organisms (animal and vegetable) illustrative 

 of fresh-water and marine life, is to hand. It 

 includes illustrative descriptions of Bacteria, Astc- 

 rionella fonnosa, Siirirella hifrons, and various species 

 •of Gyrosigna, as well as Spirulina Jcnneri, among 

 the vegetable kingdom; and Trachelomonas bulla, 

 Telotrockidiiun crateriforme, Amcebic, Acinda grajtdis, 

 Sertularia pumila, Aglaophenia plitnia, Ophiocoma 

 neglcda, Ttibifex rividoriim, Flosailaria cornuia, 

 Folyphcmiis pedkulus, Canthocajiipius minutus, Doris 

 tuber cidatus, EoUs Landsbnrgii, &c., among the 

 animal kingdom. This part is fully up to the high 

 character which its predecessors have obtained, and 

 Mr. Bolton evidently spares no pains to please and 

 instruct his clients. 



Poison Glands in Frogs. — I do not believe 

 Ihat any frogs, French or English, has a poison 

 gland, or possesses the power, like a toad, of giving 

 out a poisonous exudation from its skin, and I advise 

 H. R. T. to read "British Reptiles," by Dr. M. C. 

 Cooke, where he will find much that is interesting 

 about both Batrachians, Does your correspondent 

 mean by "French Frog," the edible frog Faua 

 £sculeHta? — Helen E. Watney. 



ZOOLOGY. 



Parasites on Dyticus marginalis. — The para- 

 sites mentioned by your correspondent Abbot G. 

 Laker, in the February number of Science-Gossip, 

 as found by him on the Dyticus viarginalis are most 

 likely one of the immature stages of a species of 

 watermite, probably that of HydrocJioreutes globulus 

 of the family Hydrachnidse. It is parasitic only in the 

 intermediate stages of its life, being a free swimming 

 animal in its perfect state. Mr. Andrew Murray in 

 his work entitled " Economic Entomology," states 

 that the eggs are deposited in the stems of various 

 water plants, producing when hatched a little six- 

 legged animal with a la,rge heart-shaped sucker in 

 front, which might easily be mistaken for the head, 

 but for the eyes being placed on the interior margin 

 of the back. It is in this stage that they attach them- 

 selves to the various aquatic insects on which they 

 are found, doubtless to feed and undergo their final 

 changes. The mounted specimens that I have were 

 all taken from a Dyticus, and are slightly different in 

 one or two respects to those described by Mr. Laker ; 

 the difference, no doubt, arising from the fact that 

 his specimens were more fully developed and about 

 to change into the nymph or third stage. There 

 is a striking difference in the respective sizes of 

 Mr. Laker's and my own specimens. The average 

 length of mine was about n'j inch, while those of 

 Mr. Laker were giants in comparison. His are pro- 

 bably full-grown. There is one important feature 

 connected with the heart-shaped sucker in front of 

 the head, which I should like to note, that appears to 

 have been overlooked by Mr. A. Murray. He does 

 not mention in any way the two mandible-like organs, 

 situated one on each side of the sucker, close to its 

 junction with the rest of the body. So far as I am 

 able to make out, they consist of an organ composed 

 of three joints, terminating in a most terrible-looking 

 claw, with four hooks of different lengths, two of 

 them much longer, sharper and rather more curved 

 than the remaining two, which are however much 

 wider at the base. The claws are turned inwards 

 towards the centre of the sucker, somewhat after the 

 manner of a spider's fangs, and also appear to have a 

 slight downward action. The object of these organs 

 at the side of the sucker is, without doubt, to assist the 

 animal to retain its hold upon the unhappy insect it 

 may happen to select as its host, as in one of my 

 specimens a portion of the skin of the beetle was torn 

 away in removing the parasite, and which I found 

 impossible to free from the sucker without injury ; so 

 it was mounted just as it was, and one of the claws 

 can be seen apparently buried in the skin, where it is 

 sufficiently transparent to allow the light to pass 

 through. My own humble opinion is, that these 

 mandibles are used for the purpose of attaching itsel f 

 to the beetle it infests, and the sucker used to extract 

 its juices. Perhaps some other readers of Science- 



