10 MAMMALIAN DESCENT. [Lect. I, 



for following this quest — that of finding the embiyos 

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

 tlie early stages of the existing Prototheria, I have 

 no douht hut that we shall be able to see much further 

 into "that dark l^ackward and abysm of time," when 

 the Huxleyan 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 metamor pilosis. 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 tixmsformation 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. 



