20S 



HARDWICKE'S SCIENCE-GOSSIP, 



ZOOLOGY. 



Parasites on Dytiscus marginalis,— I have to 

 thank Mr. Henry Blake for his reply in SciENCE- 

 Gossir for April, to my query on this subject appear- 

 ing in your issue for February. I have no doubt the 

 parasites are the immature state of a water mite (Ily- 

 drachna). I see that Professor Westwood, in his 

 "Modern Classification of Insects," vol. i. p. 105 

 (published 1S39)— under the family Dyticidce, says, 

 "Notwithstanding their large size, these insects are 

 subject to the attacks of a minute parasite, described 

 by M. Audouin under the name of Achlysia Dytici, 

 but which the recent investigations of M. Duges have 

 proved to be the immature state of one of the water- 

 miles (Ilydrachna) and which affixes itself to the 

 thin membrane with which the upper surface of the 

 abdomen is covered." IJut I have found, since I 

 first sent the query to Science-Gossii', that in Cuvier's 

 " Animal Kingdom," edition 1854, which is also edited 

 by Westwood, there is a plate illustrating the various 

 stages of Hydrachna globulus, with a note as follows : 

 — "From the valuable discoveries lately made by M. 

 Duges, it appears that these water mites undergo meta- 

 morphoses accompanied by a complete change of form, 

 the larvrc having a very large head and six legs, whilst 

 the pupx are inactive, attaching themselves by a single 

 pair of legs to the bodies of other aquatic insects, and 

 consisting, as it were, simply of an oval bag with a nar- 

 row neck, the insect in this state having been formed 

 by M. \". Audouin into the genus Achlysia, and 

 specifically named . /. Dy/icihoxti taking up its residence 

 beneath the elytra of the water beetle (Dyticus mar- 

 jp'iialis). They also attach themselves to the slender 

 filaments composing the tails of the water scorpions 

 (Nepa and Ranatra)." The pupre figured are about the 

 size of the parasites I found on D. luargiiialis, and very 

 similar in form ; I therefore conclude they were the 

 pupa: of// glolniliis. The figure of the larva given in 

 the " Animal Kingdom " shows tlie two mandible-like 

 organs mentioned by Mr. Blake (which I should think 

 are probably the first pair of legs modified). Mr. Blake 

 asks whether I "noticed the mandibles attached to 

 the sucker, and also if the legs were still present, 

 as in the nymph stage they are absent." This should 

 evidently read "pupal stage." I did not observe the 

 mandibles and there were no legs visible. Doubt- 

 less the " mamlibles " were sunk in the substance of 

 the dyticus, and 1 was unavoidably prevented from re- 

 moving the pupa- from the beetle. The second order 

 of Arachnida (Tracheari.x) to which these Hy- 

 drachncc belong, is described in the " Animal King- 

 dom " as receiving the "air by two spiracles," and 

 probably the circular-shaped dots mentioned by Mr. 

 Blake as placed "on each side, and also on the hinder 

 margin of what I may term the cuirass," were the eyes 

 and spiracles respectively. I did not observe these on 

 the pupx- present on the Dyticus marginalis, but I have 



seen very similar parasites on the water bug (Ranatra 

 linearis) but much smaller, being about 5':, of an 

 inch long, and drawn to a point at the extremity of 

 the body (those on D. marginalis being rounded like 

 a bag), on these small pupce there were two small 

 dark dots on each side. The small parasites which 

 are evidently pupae, probably of another species of 

 water mite, were situated (on one specimen) not on 

 the tail of the Ranatra, but on the under side of the body, 

 and on the first pair of legs. Now it has occurred 

 to me that, in the case of the parasites on D. margin- 

 alis they would from their position on the back of 

 the beetle under the elytra, come in contact with the 

 air stored there by the beetle for its own respiration ; 

 but the parasites on Ranatra were placed where they 

 would not come into direct communication either with 

 the air at the surface of the water, or with that 

 breathed by the Ranatra, because that insect only 

 protrudes the tip of its long tail above the surface, 

 its body and legs being constantly immersed. How 

 therefore, do these parasites obtain their supply of 

 air ? I see there is a note in the " Animal Kingdom," 

 " that some species of these Arachnida (Trachearia:) 

 such as the pycnogonidoe, do not exhibit any spi- 

 racles, and their mode of respiration is unknown," also 

 " some aquatic larvae have a very peculiar respiratory 

 apparatus." If these parasites cause the death of 

 their hosts surely they must perish with them. 

 Perhaps some of your correspondents have reared 

 Hydrachnre from pupre or larvte, and may be good 

 enough to communicate the result of their experience. 

 — Abbot G. Laker. 



Cross between Bullfinch and Canary, — It 

 has been asserted by some breeders of cage birds 

 that the canary and bullfinch when paired together 

 never produce offspring, but a pair of these birds, 

 possessed by Mr, William Yeoman of Thomer 

 near Leeds (one of two pairs which he has now on 

 hand), have this year hatched two birds of the crossed 

 species, the produce of separate broods. The first of 

 these however died soon after being hatched, but the 

 second is this day (August 5th) four weeks old, and 

 is a very fine thriving bird. This is only the fourth bird 

 of the kind which has resulted from pairs kept by 

 Mr. Yeoman for a period of thirty-three years. The 

 first which rewarded his perseverance was hatched in 

 1870, and gained a first prize at an exhibition of cage- 

 birds held at the Crystal Palace, Sydenham, in 

 February 1871. Since that time he has constantly 

 had two or three pairs of the two species on hand, 

 which have regularly associated and paired, but with 

 no result, except barren eggs, till the present year, 

 and another case which occurred about eight years 

 since, when a brood of eggs produced one very short- 

 lived bird.— 7, W. 



Water Spiders. — In reply to Mr. J. A. Ollard's 

 query in Science-Gossip for August concerning 

 water spiders. I would inform him, presuming he 



