264 STUDIES IN THE EVOLUTION OF ANIMALS 



womb and then brought forth, and oviparous means first brought 

 forth and then hatched outside. We know that there are both 

 oviparous and viviparous fishes. We have some indication that this 

 so-called archetypal hand or foot may have commenced as low 

 down as in the fishes ; for Fig. 91 {a) would seem to indicate 

 distinctly, in this Fish's foot, the beginning of a limb with five 

 digits, which is not very different, externally at least, from the foot 

 of the mammal, {b). Then the pectoral fins of shore-fishes and 

 land-fishes, with six or more digits, or what would correspond to 

 digits, as shown in {c), (d), (e), are very suggestive. In some verte- 

 brates we call these limbs pectoral and ventral fins, while in others 

 we call them hands and feet ; many zoologists, however, consider 

 them homologous. 



Few, I imagine, would deny that the pelvic fin of Rata clavata, 

 shown in Fig. 91 (/"), does not foreshadow the hand and foot 

 of the higher animals. Between the two outer big digits there are 

 many embryonic digits, some of which are not at all dissimilar to the 

 dwarfed digits of the Kangaroo foot {Macropus Bennetii), shown 

 in Fig. 122 of Sir William Flower's Osteology of Mammals. 

 Whether the minute digits of this Kangaroo have been degraded 

 from a fully developed five-digited limb, or whether they originated 

 from some fish-like limb, and have never been promoted into 

 useful digits, I leave for others to decide. 



The duck-billed Platypus is a marsupial of very low type, and 

 a good swimmer. Is there any good reason for supposing that it 

 could not have been evolved from some fish-like vertebrate, with 

 fins like those of the land-fish ? We know that certain fish can 

 breathe both by gills and by lungs ; and we know that the Frog, in 

 its early life, is a fish-like animal, breathing by gills, and in its later 

 life it is amphibious, and breathes by lungs. 



It is not easy to get rid of the notion that in this Lophius and 



