252 PEOCEEDINGS OF THE ACADEMY OF 



Dinotherium, and soon shed; they are also early shed in Mastodon and Stego- 

 don (insignis Falc. Caut.) and are not known to exist in the succeeding 

 types ; the acceleration of succession of teeth has caused them to be entirely 

 omitted. The young tooth of Elephas moreover is represented by a series of 

 independent parallel lamina? at first, which, when they unite, form a series of 

 crests similar to the type of the genus Mastodon and others of the beginning 

 of the series. The deposit of cementum takes place later, till the valleys are 

 entirely filled up. Thus the relations of this part of the tooth structure in the 

 series are also those of the successional growth of those of Elephas, or the ex- 

 treme of the series. 



It would be only necessary to show that two distinct conditions in any of 

 these respects occurred among the different individuals of the same species of 

 any of these genera, to render a hypothesis of evolution a demonstrated fact. 



It must be here observed that great size indicates little or nothing as to 

 zoological rank. It merely indicates the expenditure of a large amount of 

 stored vegetative force in the individuals of the group, however limited, which 

 exhibits it. The greatest species are often not far removed in affinity fiom the 

 least ; thus there can be but little doubt that Elephants are not far removed 

 from the Rodents, and the Rhinoceros is near the Cony. Indeed, in the same 

 genus the most extraordinary diversity prevails, for we have a very small Ele- 

 phant of Malta, and in the Miocene of Maryland a fin-back whale not so large 

 as the new-born young of the fin-backs now living. Hence Prof. Dana's ob- 

 jection* to the developmental hypothesis, based on the great size of the 

 primal Selachians and Ganoids, has but little weight. 



7. Rathke has shown that the arteria ophthalmica of the higher Ophidians 

 is originally a branch of the arteria cereb'ralis anterior, and that it later forms 

 a connection with the arteria facialis. This connection increases in strength, 

 while the other diminishes, until finally its supply of blood is derived from the 

 facialis instead of the cerebralis. 



Rathke has also shown that the cerebral origin of this artery is continued 

 through life in the three lowest suborders of the serpents, the Scolecophidia, 

 Catodonta and Tortricina; also in the next succeeding group, the Peropoda. 



8. In most serpents the left lung is never developed ; in such the pulmonary 

 artery instead of being totally wanting, remains as a posterior aorta bow, con- 

 nected with the aorta by a ductus botalli; serpents without left lung being 

 therefore identical in this respect with the embryonic type of those in which 

 that lung exists. 



9. Dr. Lespes states that the optic region of the brain of blind cave Coleop- 

 tera, examined by him, is similar in structure to that in the blind larvce of 

 Coleoptera, whose images possess visual organs. 



f 10. Those Saurians, (Uromastix, etc.,) in which the preraaxillary region 

 is produced into a uniform cutting edge, are furnished during early stages 

 with a series of premaxillary teeth, which become gradually fused and con- 

 fluent with the alveolar margin. Hence other Acrodonts are equivalent, in 

 this respect, to the j'oung of Uromastix, etc. The same thing occurs among the 

 Scaroid and Labroid fishes. In this most natural family we find the ma- 

 jority of generic forms provided with a normal complete dentition ; in others 

 (Chaerops, Xiphochilus, Pseudodax, etc.,) the lateral teeth are gradually and 

 normally replaced by a more or less cutting edge of the mandible ; and finally, 

 in the Scarina and Odacina the entire mass of teeth and jaws are coalesced, 

 forming a beak with sharp cutting edges, the single teeth being still visible in 

 the true Scarus, while they have entirely disappeared in adult Pseudoscarus 

 and Odax.J Thus in dentition the adult Scarus is identical with not fully 

 developed Odax ; Chaerops with the teeth less confluent, equals a still younger 



♦Manual of Geology, p. 



+ See under section on acceleration and retardation. 



X Giinther on Hatteria, Philosophical Transactions, 1867, II. I had already noticed the 

 peculiar development in Uromastix, but not published it. 



[Oct. 



