D A P H N I A. 



237 



are propagated by layers and cuttings, but most are 

 increased by grafting' on the common wood-laurel 

 (D. laureola], or on the mezereum. Some of the 

 smaller sorts grow well in moor-earthy soil, prepared 

 for American plants, but most of them thrive in any 

 light soil. 



DAPHNIA (Miiller ; MONOCULUS, Linnaeus). A 

 genus of small crustaceous animals belonging to the 

 sub-class Entomottraca, order Branchiopoda, and sec- 

 tion Lophyropoda. The body is of an oblong oval, and 

 compressed form, evidently enclosed in a bivalve shell, 

 attached to the skin, having its aperture beneath the 

 body, and its hinge above the back. The head is 

 distinct, and produced beneath into a kind of snout, 

 furnished with a single central small eye. From each 

 side of the head arises a large antenna-like organ, 

 having a long basal joint, at the extremity of which 

 each antenna is divided into two long articulated 

 branches, each of which supports a number of long 

 bristles. The functions of these organs in swimming, 

 being, in fact, the only external apparatus employed 

 in this motion, has induced M. Straus to regard them 

 as forelegs, although it is evident, as Midler and Jurine 

 observed, that they represent the upper antenna; of 

 the typical crabs. And here we may take occasion to 

 notice the great difficulty existing in the determina- 

 tion of the nomenclature of these and other organs, in 

 groups of animals which recede so entirely from those 

 which, by common consent, are considered as the 

 types or normal divisions of the class and, indeed, 

 the remark is applicable in every other branch of 

 the creation. We mention this subject because Dr. 

 Johnston, the celebrated naturalist of Berwick-upon- 

 ,Tweed, has recently published some observations 

 bearing upon this view of the question in the Maga- 

 zine of Natural History, which deserve attention. 

 Speaking of one of the species of the shark parasite, 

 Pandarus alntus, he says : " The student who is anxious 

 to see how ingeniously the few and simple organs of 

 this creature can be analysed and resolved into parts 

 corresponding with the complex organs of the crab \ 

 ami lobster, must consult the interesting memoir of j 

 Milne Edwards (in the Dictionnaire des Sciences j 

 Naturelles, vol. 28). I must acknowledge that the 

 analogies seem not a little imaginary, and the nomen- 

 clature derived from them is at least faulty, in so far 

 that it gives, or is apt to give erroneous ideas relative 

 to function ; the feet-jaws are not subservient to man- 

 ducation in any way ; the animal is suctorial, and 

 requires no jaws, and these organs are used solely to 

 obtain fixedness of place, while the thoracic feet again 

 are not organs to walk or creep on, but are only cal- 

 culated for swimming, which, we can conceive, it may 

 often have occasion to do." Although we admit to 

 its full extent the soundness of Dr. Johnston's remarks, 

 in examining an animal per se ; we certainly do feel, 

 when investigating the same animal with reference to 

 the structure of the remainder of its class, that the 

 great difficulty with which the subject is surrounded 

 ought to make us hesitate before we condemn a series 

 of names which the strictest analogy has proved to be 

 correct. Let us, however, look at the matter with 

 reference to some of the better known examples of 

 the class. Examine a lobster and a crab, and the 

 mouth is found to be externally composed of several 

 pairs of flattened organs, having a transverse motion, 

 and evidently acting as jaws, whilst the large pair of 

 fore legs is terminated by great and powerful claws. 

 Now, examine a spiny lobster (which is not uncom- 



monly to be met with in the fishmonger's shop, belong- 

 ing to the genus Palm urns], and the claws are no 

 longer to be seen ; in their stead a pair of limbs are 

 found, having indeed the same number of joints as 

 claw-legs, but formed like the following legs, and 

 evidently being employed in locomotion. But will it 

 be said that the least stretch is, given to our fancy 

 when we assert that the leg of the Palinurus is the 

 claw of the lobster in a modified state of development, 

 or that the former analogically represents the latter ? 

 Should we incur the chance of ridicule if we describe 

 the claw of the lobster as a leg, although it be em- 

 ployed only in prehension, and not in locomotion ? 

 Let us, however, now examine one of the little leap- 

 ing shrimps, so common on the sea coast, and of which 

 one species abounds in fresh water (Gannnarvs pulex\ 

 and we find the mouth deficient in a certain number 

 of pairs of organs, but that the legs have obtained an 

 increase of the same number of pairs ; whilst the 

 examination of such genera as Sergcstes, Sicyonia, &c., 

 clearly demonstrate the transition of structure and 

 function from mouth organs to legs. Will it be said 

 that we are adopting a faulty nomenclature, because 

 we employ a term for these thus transitory organs, 

 which indicates that they are liable to this singular 

 kind of transition ? We are aware that, by the un- 

 thinking, and by those who would lead the unthinking 

 by the employment of arguments resting upon general 

 and, as we may say, vulgar observation, rather than 

 upon accurate but difficult analysis, we should be 

 ridiculed in asserting that the sucker of the butterfly, 

 and the under-jaws of a beetle, are the same organs 

 in a different state of development, and in applying 

 to both the same term ; but we contend that the argu- 

 ments which we have above brought forward are 

 applicable to one case as well as the other; that there 

 is no fanciful theory to be built upon this strict appli- 

 cation of the rules of analysis and its consequent an- 

 alogy, and that when, by the application of the former, 

 and the adoption of the latter, we arrive with certainty 

 (and here, as we said in the outset, lies the great diffi- 

 culty) at the conclusion that a certain organ in one 

 animal is the representative of an organ in another ani- 

 mal, we are at liberty in a strictly philosophic view of 

 the subject to apply to both the same name, although 

 in common parlance it is necessary, perhaps, to use 

 different terms indicating the precise functions of each 

 organ. 



Within the shell of the Dnphnia are to be observed 

 ten small leg-like organs, having the second joint 

 vesicular, the eight anterior ones being terminated by 

 a dilated joint, margined with hairs, and serving as 

 oars, the anterior pair appears, however, to be em- 

 ployed more especially in prehension ; the posterior 

 pair of legs is differently constructed. By a curious 

 provision the eggs are deposited in a dorsal kind of 

 pouch beneath the shell within which they are hatched ; 

 at the end of the fifth day the young have acquired 

 sufficient power to take care of themselves, and are 

 expelled by the female. 



These animals, of which there are numerous species, 

 are found in fresh and standing water, where they 

 swim about with very great agility, their large branch- 

 ing antennae giving them a curious appearance, hence 

 they form interesting objects for the microscope. 

 Their history has been traced, notwithstanding their 

 minute size, by several eminent observers, the works 

 of Messrs. Schaeffer, Ramdohr, Straus, and the elder 

 .lurine may be especially mentioned. By Swammer- 



