204 THE DESCENT OF MAX. [Paut I. 



glance, apparently consisted of a group of marine ani- 

 inals,°' resembling the larvas of existing Ascidians. These 

 animals probably gave rise to a group of fishes, as lowly 

 organized as the lancelet ; and from these the Ganoids, 

 and other fishes like the Lcpidosiren, must have been de- 

 veloped. From such fish a very small advance would 

 carry xis on to the amphibians. We have seen that birds 

 and reptiles were once intimately connected together ; and 

 the Monotremata now, in a slight degree, connect mam- 

 mals with reptiles. But no one can at present say by 

 v.diat line of descent the three higher and related classes, 

 namely, mammals, birds, and reptiles, vrerc derived from 

 either of the two lower vertebrate classes, namely am- 

 phibians and fishes. In the class of mammals the steps 

 are not difficult to conceive which led from the ancient 

 i\Ionotremata to the ancient ^Marsupials ; and from these 

 to the early progenitors of the placental mammals. Wg 

 may thus ascend to the Lemuridce ; and the interval is not 

 wide from these to the Simiada?. The Simiadjc then 

 branched ofii" into two great stems, the New World and 

 Old World monkeys ; and from tlie latter, at a remote 



-■' All vital functions tend to run their course in fixed and recurrent 

 periods, and with tidal animals the periods would probably be lunar ; for 

 such animals must have been left dry or covered deep with water — sup- 

 plied with copious food or stinted — during endless generations, at regular 

 lunar intervals. If, then, the vertcbrata are descended from an animal 

 allied to the existing tidal Ascidians, the mysterious fact that, with the 

 higher and now terrestrial Yertebrata, not to mention other classes, many 

 normal and abnormal vital processes run their course according to lunar 

 periods, is rendered intelligible. A recurrent period, if approximately 

 of the right duration, when once gained, would not, as tixv as wc can 

 judge, be liable to be changed ; consequently it might be thus transmitted 

 during almost any number of generations. This conclusion, if it could 

 be proved sound, would be curious ; for we should then see that the pe- 

 riod of gestation in each mammal, and the hatching of each bird's eggs, 

 and many ether vital processes, still betrayed the primordial birthplace 

 of these animals. 



