1068 EEPORT OF COMMISSIONER OF FISH AND FISHERIES. [88] 



of bone], siicli as we actually find to result in the two cases under con- 

 sideration, and as happens in a few of the posterior trunk-segments 

 (sacral) of birds and mammals. Embryology and phylogeny both bear 

 out these conclusions. Not only do the vertebral centra become more 

 rudimentary as the young condition is departed from during the life- 

 history of the individual tortoise, but the centra also become successively 

 more rudimentary as we pass from the less completely armored genera 

 Sphorgis and Tnonyx, to the more completely armored Tesiudo and Cis- 

 tudoJ^ 



The data respecting the mode in which the primitive membrane of the 

 rays of fishes is fractured and thus segmented evidently apply to the 

 genesis of vertebral bodies the membrauous basis of which invests the 

 chorda as a coniinuum at first, its continuity remaining unbroken on 

 the inferior face of the trabeculse cranii, where it gives rise to the para- 

 sphenoid bone of fishes. The points of fracture of the osteogenetic 

 membranes investing the chorda, which herald the subdivision of said 

 membrane into the foundations of vertebral bodies, correspond homo- 

 nomously in position with the intermuscular septa between the myo- 

 tomes. These phenomena probably never occur till the embryo begins 

 to make voluntary movements in the egg, egg-follicle, or temporary 

 uterus in the lowest forms ; such at least seems to be the case with the 

 embryos of the Ichthyopfiida* Such interpretations of the genesis of 

 structure bring the phenomena of development under the domination 

 of natural law, and accept little or nothing in common with old-fash- 

 ioned teleology, that inane creation of mystical metaphysicians, whose 

 anthropomorphic preconceptions have hindered the progress of biolog- 

 ical science for not less than two centuries. 



Looking in an unprejudiced way upon a living body, we are forced to 

 admit, after the strictest investigation, that its ''vitality "is only one of 

 man}' special modes in which matter may exhibit phenomena of motion 

 or action. If life is a continuum in virtue of the fact of the production 

 of germs, from which new and similar organisms may grow ; if likewise 

 the energy of an actively living, growing body is continuously exhibited, 

 then that energy must be continuously expended, and food must be 

 constantly appropriated, and as constantly must there be material waste 

 in progress. 



Kewton's third law of motion states that "Action and reaction are 

 equal." If, therefore, it is true that the body is continuously in action, 

 it must be true that there is continuous reaction going on in the most 

 ordinary voluntary physiological work done by the body. Further, we 



*It is of some interest to note in this connection that distinct diarthrodial articu- 

 lations of the heads of the ribs with the vertebral bodies never occurred in the Verte- 

 brates until the differentiation of the pneumatic respiratory apparatus. This artic- 

 ulation is changed to a sutural one in the Turtles, in conseqiaence of the suppression 

 of the thoracic respiratory movements of the ribs by the development of the rigid 

 carapace to which the latter become fused. 



