[88]

June 25— 1843 —

After having read some notes of Waterhouse on Mammals‒ I see that there are very few intermediate links between families, indeed such a half-way link wd form a new family. The link can generally be classed on either one, or other or third side. By my theory families far apart, have descended from some remote stock & there never will be any forms intermedial between the two, but between each, perhaps very different & the common centre.— this is important.— Hence we shd never find an exact half way between Rodents & Marsupials but between their latter & some unknown form I argue against circles, but if Marsupiata were like parent form, then you might as inevitably giving idea of groups of equal value, which is an assumption without standard of comparison.— The circles touching represent equal affinities — this is at bottom of probability of Quinarian system.— I suspect alliance of the links to other families is by saltus of a certain organ, thus Owen has discovered that vagina of Bizcacha is divided in Rodents, one

[88v]

of the group taken as a whole near the Marsupiata, & thus of this group the Bizcacha has one character much nearer.— How is this? Is each part altered separately by selection? or old character retained?

Waterhouse thinks most of the affinities between the great families are "adaptive".

This term vague & requires definition. Thus wombat is supposed to lead off by its teeth to Rodents, but teeth of Wombat really an Marsupial structure, but form of teeth merely adaptive.— The characters drawn from such parts as are common to several forms with different habits are best sign of real affinities & not being adaptive — thus vertebrate structures & such peculiarities in teeth as run through whole of Marsupiata— though here we get into vagueness, for

[89]

there seems some remote affinity between Marsupials & Rodents.—

 

Number of species ie variations on one common type. I suspect silently comes into play in classifying.— Waterhouse says zoologist classify by "rule of thumb".—

W. says that at bottom! of large groups characters wider apart — from this argument he wd put Marsupials into Mammalia & not mark them groups of equal value wh is absurd, I think — says same thing occurs in Reptiles—

W. says (in Zoolog Proc. 1841?) Tarsipes rostrata an extraordinary Marsupial with scarcely any teeth described.— Is not this Honey Sucker??