576 THE POPULAR SCIENCE MONTHLY, 



have no proper union, no true articulation with the spinal column. 

 Even in those cases where the bones of the pelvis and of the sternum 

 are most securely fastened to the neural axis, it is by a mere anchy- 

 losis completed only in the adult age. 



The dermal system is the counterpart and homologue of that won- 

 drous external skeleton of articulata, as you must see if you have fol- 

 lowed me through the metamorphoses of ccelenterata, entomostraca, 

 and cirrhipeda to mollusca, and from mollusca to vertebrata. Com- 

 parative anatomy will not hesitate now to point out every correspond- 

 ence of every part, every organ, every articulation. Not a bone, nor 

 a scale, nor a hair, is ever lost. In each limb there are so many joints 

 and no more ; and with a certain definite relation to each other, clear 

 and true ; to be seen in the contorted limbs of articulata, as well as in 

 the arm of man. 



Our very limited amount of time compels me to make this address 

 a mere introduction to the subject ; compels us to be content with 

 mere suggestions for studies in biology, to be pursued by after-inves- 

 tigations. 



One of these suggestions is made to us by the manner of the fold- 

 ing of vertebrate limbs. The difficulties of the question, as put by 

 Dr. Wyman, for example, are well worth consideration, and by this 

 transcendental history of evolution find solution. How is it that in 

 all vertebrates the forward limbs fold one way, forward, and the hind- 

 er limbs the reverse ? But take you any two segments of an articu- 

 late creature, a crab or a grasshopper, and observe how the append- 

 ages extend away from the body, and the mystery is explained. For 

 the effect of the magnetic and other forces causing polarity or arrange- 

 ment is to be searched for and found first in the segments, always 

 remembering that in articulates the axis of the neural system — the 

 life of each segment — is transverse to the general axis of the com- 

 pound organism. Now, separate two such segments of your articulate 

 — fold them together in the manner indicated by the history of cypris 

 and of lepas — revolve the involuted creature ninety degrees, stretch the 

 limbs forward and backward as their organization fits them to move ; 

 and you cannot fail to perceive a perfect counterpart of the motions of 

 vertebrate extremities. 



But this is not half the demonstration. Indeed, it is now so well 

 settled, that Science can, dare make one of tho^Q 2?redictions always re- 

 garded as affording by their verification the highest order of certainty. 

 After noticing the remarkable fact that all vertebrates having limbs 

 .have four, or the rudiments of them, and no more, Science predicts with 

 the repose of conscious systematic truth, derived from this doctrine of 

 segmental genesis, that no vertebrate animal, nor the remains of any, 

 ever will be found, on the earth, or in the waters under the earth, or in 

 its caverns or quarries, having more than these four homologous ap- 

 pendages — and these always dermal. 



