1 MAMMALIAN. DESCENT. [Lect. I. 



for following this quest — that of finding the embryos- 

 of the Monotremes. If they succeed, and we can get 

 the early stages of the existing Prototheria, I have 

 no doubt but that we shall be able to see much further 

 into "that dark backward and abysm of time," when 

 the IJuxleyan Hypotheria did duty for the existing 

 Mammalia. 



I shall show in these lectures that some of the lower 

 kinds of Eutheria (placental mammals) undergo, in 

 their pre-natal state, and also during their infancy and 

 youth, most remarkable transformations. I use the 

 word transformation in a popular sense, as the term 

 "metamorphosis" has a very limited and absolute 

 meaning in science. 



All the animals above the Protozoa (first creatures) 

 are called " Metazoa," because they undergo remarkable 

 changes of form, beyond their first stage or state. 

 When these various stages are gone through in the 

 active condition — the partially developed animal leading 

 for some time a free and out-of-door life — it is said to 

 undergo metamorphosis. If these changes are not 

 utilised, if they are pre-natal, and the new-born active 

 creature is practically the same as the adult, the more 

 familiar word transformation is employed for the unused 

 early changes. 



A Snake undergoes remarkable transformation whilst 

 in the egg ; a Frog is marvellously metamorphosed during 

 its active life. 



