May 2 2, 1879] 



NATURE 



81 



to 250, plunging this same bar into ordinary cold water 

 reduced its value to 130 ; thus the mere difference of the 

 normal temperature of the air in the room and water which 

 had been in this room some hours produced 20°of difference. 

 In fact, I found that the radiant heat from the hand would 

 raise the magnetic value several degrees, and thus nickel 

 may be regarded as a magnetic thermometer far more 

 sensitive than the ordinary mercurial centigrade. 



The instrument also measures the^ electrical resistance 

 of wires or fluids. In order to make it do this we have 

 only to place the resistance to be measured across the two 

 wires of one induction-coil and on the other known resist- 

 ance units. In this way we can produce a perfect balance, 

 for it then becomes an induction bridge, the results and 

 modes of testing of which are somewhat similar to Wheat- 

 stone' s bridge. 



It measures also the electrostatic capacity of Leyden 

 jars or condensers, and is sufficiently sensitive to appre- 

 ciate and measure a surface of tinfoil not larger than four 

 inches square, the condenser being simply placed between 

 the wires of one pair of coils, and the disturbance pro- 

 duced being measured on the sonometer. 



I could cite many more interesting experiments in other 

 branches of physical research for which this instrument 

 offers a wide field of observation ; but my object this 

 evening is neither to broach new theories nor to correlate 

 at present the results obtained with views already ad- 

 vanced by Ampere and others. 



My only desire has been and is to show the wide field 

 of research the instrument opens to physical inquirers. I 

 trust that in more able hands it may serve to elucidate 

 many physical phenomena. 



ON THE EVOLUTION OF THE VERTEBRATA i 

 III. 



f^ROCODILIA. — The crocodiles form another group 

 *-^ of reptiles which has become isolated from all the 

 contemporary groups or orders. The most perfect anti- 

 thesis of the bird, the crocodile, is, nevertheless, in essen- 

 tials, in strict conformity with the bird pattern ; or, 

 rather, both it and the bird conform to the pattern of 

 some ideal or vanished reptile. 



This likeness can be shown in the body, but it is most 

 evident in the head ; although unlike the bird's skull in 

 general specialisation, that of the crocodile is, in all 

 essential respects and in numberless details, like that of a 

 young bird. Compare the strong, solid, and dense skull 

 of the crocodile, with its thick, pitted, and rugose bones, 

 and accurate and dentated sutures, with that of a parrot, 

 a toucan, or a hornbill — scarcely a suture left, the bone 

 looking like polished ivory and the substance so com- 

 pletely spongy within that its weight is but little more 

 than that of ja few quills of the same bird. Yet these 

 lightest and most delicate of all skulls had once all the 

 sutures seen in that of the crocodile, and the two types of 

 skull developed each "centre" in the same manner and 

 on a similar model ; in the middle of the incubating 

 period they were so much alike that one diagram might 

 have served to illustrate both. 



In their covering, as well as in their general form, the 

 crocodiles contrast strongly with the birds ; instead of a 

 soft plumage, often gorgeous in colour, they are invested 

 with a coarse armour of segmental rows of rough plates 

 of bone (dermostoses), coated over with horn. Repre- 

 sentatives of the turtle's plastron are seen in the so- 

 called abdominal ribs — which must not be confounded 

 with like structures of the same name seen in the cha- 

 maeleon and Hatteria — and in the inter-clavicle, which is 

 fixed to the under-surface of the breast-bone. 



The frame-work of the body is well ossified in the 

 adult, and the vertebrae and ribs are very similar to those 



* Abstract of Prof. Parker's Huntcrian Lectures, delivered at the College 

 of Surgeons, commencing on February lo. \ Continued fnii p. 64. 



of a bird, the greatest difference being in the neck, which 

 is much shorter and stouter, and has [much larger rudi- 

 mentary ribs, which remain permanently distinct. In the 

 young of the7?a//to(Emeu,&c.), however, all the cervical 

 vertebrae except the atlas and axis, have a pair of ribs, 

 which remain distinct for a considerable time in the 

 upper part and permanently in the lower part. The cro- 

 codile's sacrum also, instead of being composed of a large 

 number of joints, has merely two, that carry the pelvis, 

 whilst the tail, instead of being arrested, as in living birds, 

 is developed, as in the ancient Archaopteryx. The ver- 

 tebrae of the crocodile are for the most part procmlous 

 (concave in front and convex behind), and thus resemble 

 those of the dorsal region of plovers, penguins, and some 

 other water-birds. The setting in of the ribs and their 

 overlapping {uncinate) processes are also similar to what 

 is seen in birds. 



The rhomboidal sternum is cartilaginous, and sends 

 out behind a pair of xiphoid processes, being defended in 

 front by the bony interclavicle, which is the counterpart 

 of the leg of the Y-shaped merrythought of the fowl. The 

 shoulder-girdle is composed of a pair of cartilages virith a 

 gentle curve and of a moderate width ; each is ossified by 

 two bones, an upper, the scapula, -and a lower, the 

 coracoid. 



In the head, all distinction between dermal scutes and 

 sub-cutaneous bones is lost ; a thick web is ossified 

 throughout, and has only left a thin layer of the skin soft, 

 as a "quick" to the horny coat. From the snout to the 

 exit of the optic nerves, the internal cranium is unossified, 

 while the posterior part is well ossified, as are also the 

 basal region up to the pituitary body, the capsules of the 

 ear, and the alisphenoids. The labyrinth of the nose is 

 very simple. A hard palate is 'formed by the maxillaires, 

 palatines, and pterygoids, thus causing the nasal passages 

 to open far back in the throat, this specialisation being of 

 advantage to the crocodile while drowning his prey. 



The structure of the organ of hearing agrees with that 

 of the tortoises and the higher lizards, the drum cavity 

 being formed inside the quadrate, into which an air-tube 

 {siphotiium) opens into the mandible, as in birds. The 

 two drum cavities communicate in a passage running over 

 the skull behind. A rudiment of this passage exists in 

 birds, and in the higher kinds opens into the spongy 

 tissue which lies between the two tables of the skull. 



Birds. — The lower tentative forms of birds have 

 for the most part evidently come and gone during the 

 time the crocodiles have been in existence. The palaeon- 

 tologists, however, are beginning to show us how tho- 

 roughly intermediate between the true reptiles and birds 

 the extinct birds of the chalk and the oolite were. The 

 most ancient or generalised types of living birds, the 

 ostrich tribe, are all incapable of flight, but the oldest 

 bird known in the fossil state — Archaopieryx — was well 

 fitted for flight. 



Interesting connecting links between the ostrich tribe 

 and the higher forms are seen in the southern world 

 {Notogoea), where many of the birds have a much lower 

 and more reptilian structure than their northern relatives, 

 their power of flight being less, their brain smaller, and 

 in many cases they are deficient in the inferior larynx or 

 syrinx. Thus the South American Tinamous, which are 

 intermediate between the ostrich tribe and the grouse, 

 have a very small brain, and consequently such low intel- 

 ligence that they have not the sense to use their own 

 wings ; moreover, their flesh resembles that of a reptile, 

 they possess lacertilian super-orbital bones, and a con- 

 siderable number of the sutures in the head remain per- 

 manently open. These birds do not so much resemble 

 the South American Rhea as the Australian ApUryx, 

 representative species being often found in these two 

 regions which correspond with each other, but are far 

 more ancient than, and do not correspond with, the types 

 found north of "Wallace's Line." 



