1890.] MR. W. K. PARKER ON OPISTHOCOMUS CRISTATUS. 45 



beast ever became transformed into the quick, hot-blooded, feathered 

 fowl, the joy of creation. 



Now if any one will look at the picture I have made of the half- 

 ripe embryo of the Hoatzin, he will see that which will help him to 

 imagine how the Reptile crept out of his lowliness and became that 

 high and noble creature — a Bird. 



Of course the wings dominate everything else in the organization 

 of the bird ; all other parts must be correlated to these metamorphosed 

 paws. That wings were paws we see in this Reptilian bird, and the 

 suppression of the parts of a five-fingered hand, which is so striking a 

 character in the normal wing of a bird, whereiu three digits only, and 

 these strangely mangled and fused, are all that remain of the Rep- 

 tilian fore-foot. That suppression is incomplete in Opisthocomus. 

 In the half-ripe chick of tiiis bird, the first and second fingers have 

 claws as large, or nearly as large, as those of the toes ; and on the 

 third finger, which, as a rule, in birds has only one phalanx, instead 

 oi four (as in the Reptiles), I found in one of the embryos a definite 

 claw, such as I have shown to exist in Struthio and Rhea ; I have 

 seen this in no other bird but these three. There is, also, what 1 have 

 found in many birds, a rudiment oi \\\q fourth finger ; this is a "pha- 

 lanx " in this bird, it is a " metacarpal " in the chick of the common 

 fowl and in the Carinatse generally. 



In Opisthocomus, and in a few other birds, the two normal proxi- 

 mal carpals, those that in the adult bird are always free and mobile, 

 are, for a few days, segmented into additional elements. Thus, 

 taking what I find in this and other birds, the bird's wrist may have 

 all the carpals seen in Amphibia and Reptiles. I am familiar with 

 nine carpals in the wrist of birds, although normally only two are 

 permanently distinct. 



If these facts are not remarkable, I know of nothing that one need 

 wonder at and admire ; they cannot be made into poetry, but they 

 are not prosaic. Nor are there wanting, in this bird, as in others, 

 signs oi marginal and intercalary digits in the wing of the embryo; 

 atavistic remnants or vestiges that are Reptilian and probably Am- 

 phibian "stigmata." Rut the more fused proximal structures that 

 help to form the organ of flight in this bird are as remarkable as 

 the free distal parts. 



This bird, which I take to be an archaic Curassow, an unchanged 

 "waif" of the family from which the Cracidce arose, like the 

 Tinamou, never lost its sternal keel ; the Ratitae have lost it : they 

 are overgrown, degenerate birds that were once on the right road 

 for becoming flying fowl, but through greediness and idleness never 

 reached the " goal," went back, indeed, and lost their sternal keel 

 and almost lost their unexercised wings. 



Now the Tinamou has lost its tail, or nearly so ; the Hoatzin has 

 kept its tail ; the former, to make up for this, has a huge keel in his 

 extremely long sternum, whilst the Hoatzin has a small keel on a 

 short sternum. 



Both of these birds can fly a httle, they are not careful to culti- 

 vate that talent, they are not birds of " understanding." Now the 



