ClIAP. III. 



YOUNG TURTLES. 



391 



These facts show plainly, that there is a common plan of development m all 

 Testutlinata, however much they may differ m their full-grown .state, and that 



agents as far as llicy liniil tlio growth of aiiiinals and 

 j)lants ; nndcr artilicinl r<'strainl, llial iiniHiscd by 

 man.) The next sici) in tlic development unfolds tlie 

 prominent featnres of the braneh of the animal king- 

 dom to wliieh tlic new lieinK belongs. It marks the 

 sphere in wliieli it is to grow up. At this stage the 

 jdan of the development characteristic of the branch 

 is, as it wei-e, laid out, and its direction and ten- 

 dency are defined; but the manner in which this is to 

 be accomplished remains to be seen in the further 

 progress. What unexpected resemblance to the moral 

 and intellectual development of Man ! 



We might next expect that the mode of execution 

 which characterizes classes should necessarily follow, 

 but this is not so. Just as in other developments, the 

 true character of the structure is frequently not ap- 

 parent before it is completed : certain complications, 

 which arc embodied in it, become visible before their 

 relation to the whole can be perceived ; the form of the 

 structure may also be recognizable before its consti- 

 tutive elements can be analyzed ; many details in the 

 structure, the relative proportions of the parts to one 

 an(j|lier and their relations to the surrounding circum- 

 stances, may be fully or partially worked out long be- 

 fore the distinguishing character of the structure, as a 

 whole, is appreciable. 



This, also, is precisely the case with the develop- 

 ment of different animals. In Turtles, which as Rep- 

 tiles are cold-blooded, air-breathing, oviparous ani- 

 mals, none of the most prominent characters of the 

 class are developed before they are lialebcil, (as, for 

 instance, their aerial mode of breathing ;) wliile some 

 of these class characters are only recognizable in a 

 much later period of life, (their oviparity, for in- 

 stance.) Yet, as showing the manner in whieii the 

 plan of structure of their branch is carried out, these 

 diameters are truly class char.ncters. On the con- 

 trary, the special complication of that structure which 

 characterizes the order as :in order, — the separation 

 of the body into distinct regions, a head, a neck, and a 

 tail, and the presence of the shield and the four legs, 

 which appear very earlj', even before the animal has 



assumed its form, — shows plaiidy, that in Testudinata 

 the development of the ordinal characters precedes 

 not only that of the characters of the famih-, but also 

 that of the characters of the class. Strange as it may 

 appear, it is uiujuestionable that in Turtles the ordinal 

 characters are develo[)ed before those which charac- 

 terize tlie class. The early separation of the liead 

 from the neck ; the distinctness with which the limits 

 between the neck and trunk, and between this and 

 the tail, may be recognized, almost as soon a-s the 

 main axis is formed ; and, finally, the early develop- 

 ment of the shield and of the four legs leaves not the 

 remotest doubt upon this point. 



Next, the form is developed, so that the most 

 prominent family character appears immediately after 

 the ordinal characters, in all the families of Testudi- 

 nata, with the exception of the Emydoidai, and prob- 

 ably also of the Testudinina, though these have not 

 yet been observed. It is particularly interesting, 

 that this character is fully marked in the Chelonioidic, 

 Trionychidoe, Chelj-droidic, and Cinosternoid;u long 

 before they are hatched ; whilst in the Eraydoidoe it is 

 not apparent for a long time, even for years after their 

 birth, at a time when they exhibit already most of 

 their generic and specific characters. As to the suc- 

 cessive appearance of the generic and specific char- 

 acters, even limiting the inquirj' to the different gen- 

 era and species inhabiting North America, much more 

 extensive investigations, than I have been able to 

 make thus far, are still required, before it can be sat- 

 isfactorily illustrated. Meanwhile I refer to my re- 

 marks, p. 290-295. The great difficulty in these 

 investigations consists in a correct appreciation of 

 those peculiarities which m.ay be embryonic and not 

 specific, tliough preserved through life, and enumer- 

 ated by herpetologists among the specific characters. 

 I c.in state, however, that I do not know a Turtle 

 wliicli does not exhibit marked specific peculiarities 

 long before its generic characters are fully developed. 

 It is only necessary to comjiare the mode of devel- 

 opment of some of the Articulata with that of the 

 Testudinata, to perceive at once how different the sue- 



