246 



KNOAATLKDGli: ♦ 



[June 1, 1886. 



prints are avian); or we must assume that, the above- 

 mentioned transformations having occurred partly in Palfeo- 

 zoic times, the passage from reptile to bird was eflected 

 during a yet eai-lier period of that epoch. The former 

 is a gi-atmtous and needless, even if it be not a pre- 

 posterous assumption; while, as regards the latter, atten- 

 tion must be drawn to the reptilian character of the Meso- 

 zoic birds; how in the Trias we find them addicted to 

 quadrupedal habits; in the Jurassic, using the claws of 

 theii- anterior extremities (probably) for "catching hold"; 

 here but partially or not at all feathered, there well arrayed 

 with teeth, and so on ; everywhere, in brief, announcing 

 themselves as undergoing a contemporary evolution. 



In fine, if " certainly " be a fit expression to employ 

 in dealing with a subject about which an authority like 

 Prof. Seeley is so little sanguine, it would be preferable 

 to summon it after reversing the order of succession an- 

 nounced by the authors of the " Story of Creation," as 

 given in the first chapter of the Pentateuch, and the March 

 issue of Knowledge. 



PLEASANT HOURS WITH THE 

 MICROSCOPE. 



By Henry J. Slack, F.G.S., F.R.M.S. 



HE biting and chewing organ of rotifers is 

 commonly Ciilled a gizzard, but it does not 

 correspond with the gi-inding machine of 

 the fowl, or with the remarkable one of the 

 house cricket or the coarser one of the 

 blackbeetle. It is, as Gosse showed many 

 years ago, a mouth, having certain resem- 

 blances to the tiophi, or mouth organs, of insects, which are 

 composed in the well-developed instances of beetles of two 

 mandibles, or chief jaws, two maxillaj, or lesser jaws, and an 

 upper and lower lip. If the student will examine these 

 pai'ts in a biting beetle, and then look at the mouth 

 apparatus of a gnat, a flea, a bug, a butterfly, and a blue- 

 bottle, the first impression will be that each one belongs to 

 an entirely different plan. The beetle is evidently a biter 

 with cutting and tearing forceps. It can Lite a hole in a 

 hai'd substance, but has no boring or piercing tool and no 

 .saw. The flea has excjuisite saws ; the bug, three very 

 fine lancets and a sucking tube. The gnat is not a biter ; 

 she — for the female is the tormenting one — possesses sis 

 sharp-pointed lancets, two of which (the maxUla?) have some 

 sawlike teeth at the top. There is also a long, stout, cylin- 

 drical piece ending in a cleft knob, like the opening bud of a 

 flower. All these parts can be ti'aced as modifications of 

 the corresponding parts of the mouth of a biting beetle. 

 The stout long cyhnder is an immense prolongation of the 

 lower lip (labium), the lancets are modifications of the 

 mandibles and maxillse, and so on. The bluebottle's mouth 

 is formed as a sucking machine of another type. It is 

 remarkable for a number of partially open tubes — modified 

 trachese — and this sort of construction is carried to a 

 wonderful extent in the Daddj- Longlegs gnat, which has 

 over three hundred of them. 



Speaking generally, when any organ shows a capability 

 of considerable modification, some species of creature is 

 sure to exist in which the modified organ is so widely 

 difl'erent from the simplest form in which it is known that 

 the resemblance (homology) can only be traced bj- studying 

 the intermediate gradations. 



The rotifer's mouth, which can only be thrust out in some 

 species, is a biting and chewing machine, exhibited bj' 

 the pitcher rotifers, or Brachions, in the greatest per- 



fection. Let us examine one of them with Mr. Gosse's 

 a.ssistance. Fir.^t there is a globular bag which contains 

 and moves the various parts by means of appropriate 

 muscles. There we find the parts shown in. the annexed 

 view (tig. 1), borrowed from Gosse. The muscular bag a 

 he calls a masta.c, which means mouth or jaws ; 6 is a com- 



plex piece, the malleus or hammer ; c, its handle (manubrium) ; 

 at fi is a joint articulating the handle to e, the uncus or 

 hook ; / is another complex piece, forming the incus or 

 anvil, being the part on which the hammers strike ; 

 g (lettered only on one side) represents two pieces — rami, or 

 branches — hinged on to !i, the fulcrum, so as to open and 

 shut. The motions of all these parts when in action are 

 very complicated. What may be called the toothed or 

 ribbed heads of the hammers come together and fall on the 

 corresponding parts of the anvil, which has its own motions. 

 This wonderful organ can exercise some choice, and if an 

 impracticable or unfit substance gets in the handles give a 

 sudden twist and toss it out. 



In watching the proceedings of a pitchei' rotifer we 

 never witness the amount of chewing that might be ex- 

 pected from the complexity of the machine. Most of the 

 objects swallowed pass into the stomach after a few grips 

 which do not pulp them, and often do not alter then- 

 appearance. 



As in the case of the insect mouth, the modifications of 

 the rotifer mastax may be referred to more or less 

 suppression of some parts and extension of others, and, 

 whether Mr. Gosse's comparisons of the mouth organs of 

 the two groups be completely accepted or not, very interest- 

 ing and important lessons may be learnt by studying them 

 together. Fig. 2, representing the mouth of Xotommata 

 clavidata, shows a considei'able simplification of fig. 1, and 

 fig. 3, Furcularia marina, a still more remarkable divergence 



Fk;. 2. 



in the direction of simplicity. Those who wish to study 

 the various forms in detail should consult Mr. Gosse's 

 remarkable paper in the " Philosophical Transactions," * 

 illustrated by eighty-five drawings. Dr. Hudson is giving, 

 and no doubt wOl continue to supply, sketches of the mouth 

 organs of the various British species as his work progresses. 

 This monogram would be improved by giving a little more 

 information in the letterjiress, and suiiplementiug the use- 

 lessly large figures with more anatomical detail. A 

 drawing 6 inches long, showing no more than would be 

 displayed perfectly in one of 2 inches, is a mistake. It is 



* February and March 1855. 



