[41]

 (243

(43

obscure; but we may infer as it is in some degree probably probable, that all placental mammals are descended from an are the descendants of implacental ma or marsupial mammals, as these latter seems to have apparently come first in the order of Geological succession, & more especially as the marsupials clearly plainly lead to the monotremata, that is to the Ornithorhynchus & Echidna of Australia. The monotremata have exhibit a plain affinity with reptiles & birds, so that we are thus faintly obscurely guided some short way towards the progenitor of the five great order Vertebrate orders.

The Lepidosiren which has been placed by some naturalists amongst fishes & by others amongst Amphibians the Amphibians, & the Amphioxus, a fish which either has lost or never gain acquired or has lost several of the most important characters points of all the characters of the Vertebrata, gives us an obscure glimpse at into the structure if the progenitor of all the whole Vertebrates*)Kingdom.*)

[41v]

[mathematical notes by G. H. Darwin not transcribed]