228 



HARDWICKE'S SCIENCE-GOSSIP. 



[Oct. 1, 186S. 



Select a large and clean female of the common 

 water- flea, Daphniapulex, and place it in the com- 

 pressorium, where it will be retained naturally on 

 its side. The instrument should be so adjusted as 

 to render the body motionless, with the carapace 

 slightly flattened, but still giving it sufficient liberty 

 to move its antennae and limbs. Use a half-inch 

 objective, stopped to an angle of about 45°. The 

 illumination should be, at flrst, the paraboloid, with a 

 fine light. The binocular arrangement is essential, 

 and the lowest eye-pieces are the best to commence 

 with. In examining the heart under these condi- 

 tions, it is probable that the great rapidity of its 

 contractions will interfere with any useful definition 

 of its structure ; but after a while these will become 

 much less frequent and the difficulty will be removed. 



By using the fine adjustment, the focus, or plane 

 of vision, may be slowly moved from the nearer to 

 the farther side of the heart ; and if the instruments 

 are good, the specimen of fair size and clean, aud 

 the arrangement of the light carefully attended to, 

 the structure and action of the organ should at once 

 be perceived. If this is not the case, the specimen 

 should be changed, and other objectives, eye-pieces, 

 and modes of illumination tried. Some care and 

 patience will be necessary at first ; but after once 

 obtaining a good view of the heart of Daphniapulex, 

 those who have had, perhaps, some difficulty in 

 seeing it with all these appliances will find that they 

 can display the much smaller heart of D. vetula 

 with a two-third or even a one-inch power. 



It will be seen that the heart of Daphnia is homo- 

 logous to two chambers or sections of the dorsal 

 vessel of an insect ; that is to say, it has one pair of 

 vertical slits opposite to each other and approxima- 

 ting on the dorsal aspect. The blood, distinguished 

 by its suspended corpuscles, sweeps round between 

 the inner and outer surfaces of the carapace, and 

 along the upper side of the abdomen, into the 

 cardiac chamber, where it pours into the heart 

 through the two slits or valvular openings. The 

 muscular fibres of the organ are placed vertically, 

 or somewhat like the meridians drawn on the 

 artificial globe. The first part of the contraction 

 closes the slits simultaneously, and its continuation 

 expels the blood forward through a distinct anterior 

 (arterial) vessel. 



In Dr. Baird's beautifully illustrated and learned 

 work on the "British Entomostraca," he says of 

 the Daphniadae, — " On the back, in the first segment 

 of the body, we see an ovoid-shaped vesicle, pos- 

 sessed of very rapid contractions ; this is the heart. 

 According to Jurine, there springs from its anterior 

 extremity an arterial vessel, which contracts in an 

 opposite manner to the heart itself, curves imme- 

 diately from its origin, and goes backwards, follow- 

 ing the direction of the intestinal canal. 



" Gruithuisen describes the heart and circulation 

 at greater length. He says there are two hearts, 



one venous, the other arterial. The venous supplies 

 the intestines and other parts of the body with 

 blood; the arterial supplies the head and parts 

 connected with it, its branches making the circuit 

 of the shell on the anterior edge, and collecting near 

 the posterior inferior part into one large trunk, 

 which runs along the back of the shell, and returns 

 to the arterial heart again." 



I have not been able as yet to find any satisfactory 

 description of this organ, and certainly no mention 

 whatever of the wide slits opening and shutting, 

 and, like mouths, swallowing in the corpuscles of 

 the blood. I am led, therefore, at present to believe 

 that this is the first notice of the fact. Its publi- 

 cation will, however, produce a quick and sharp 

 rectification, should the assumption of its novelty 

 be erroneous. 



If it be found that nothing is said of the slits in 

 the heart of Daphnia in] the many valuable works 

 treating on the Entomostraca, I shall be inclined to 

 attribute the omission to a sort of learned contempt, 

 felt and expressed by many naturalists, for the more 

 efficient and complicated forms of microscopes. A 

 late well-known conchologist assured me that " if he 

 could see the lines on Pleurosigma angulatum, he 

 was quite content;" and one of our most dis- 

 tinguished living naturalists, to my personal know- 

 ledge, persists in the use of a cloudy old triplet, 

 with which he declares "he can see everything 

 necessary to be seen." 



The absurdity of this will be manifest to all who 

 reflect that the countless varieties of microscopic 

 objects require every possible kind of treatment 

 and illumination ; that at least all procurable means 

 of observation should be always at hand ; and that 

 no instruments can ever be considered good enough, 

 when we have to depend upon them, in the exami- 

 nation of a world as infinite in its minute structure 

 as it is vast in its extent, and which we are com- 

 pelled to believe is actually crowded with strange 

 and wonderful things, the destined novelties of 

 future ages, though old, perhaps, as the commence- 

 ment of organic life, waiting in the sublime patience 

 of nature to be discovered, but as yet unrecorded 

 and unknown. 



Kensington. H. C. Richtek. 



Oxalis named " Alleluia " (p. 210). — Before 

 the Reformation in the Church of England, and in 

 the Catholic Church at the present day, the word 

 "Alleluia" was added to the Introits, Graduals, 

 and other parts of the service, between Easter and 

 Whitsuntide. It seems likely enough that the 

 "Woodsorrel was named " Alleluia " from its blossom- 

 ing at that time ; I have before quoted Gerarde as 

 hinting at this explanation (Science-Gossip, iv. 52). 

 It has also been suggested that the use of the Wood- 

 sorrel leaf by St. Patrick may have originated the 

 name. — B. 



