76 Evolution and Adaptation 
result is in exact harmony with the well-known law of Von 
Baer, which refers to natural species, both nearly related and 
widely dissimilar. Von Baer’s observations as well as Dar- 
win’s, and as well as those of every student who has ever 
compared the embryos of two vertebrate species, may be 
summarized as follows :— 
“ Animals which, though related, are very similar in the 
adult state, resemble each other more closely in early stages 
of development, often, indeed, so closely as to be indistin- 
guishable in those early stages. As development proceeds 
in such species, the differences between the two embryos com- 
pared become more and more pronounced.” On this point, 
which is an essential one, I cannot agree with Hurst; for I 
do not think that the facts show that the early stages of two 
related forms are necessarily more and more alike the farther 
back we go. The resemblance that is sometimes so striking in 
the earlier stages is due to the fewer points there are for 
comparison, and to the less development of the parts then 
present. Hurst continues: “If similar comparisons could be 
instituted between the ancestral species and its much modi- 
fied descendants, there is no reason for doubting that a similar 
result would be reached. This, indeed, has been done in the 
case of some breeds of pigeons, which we have excellent 
reasons for believing to be descended from Columba Livia. 
True, C. via is not a very remote ancestor, but I do not 
think that will vitiate the argument. Let me quote Darwin 
verbatim: ‘As we have conclusive evidence that the breeds 
of the pigeon are descended from a single wild species, I 
have compared the young within twelve hours after being 
hatched ; I have carefully measured the proportions (but will 
not here give the details) of the beak, width of mouth, length 
of nostril, and of eyelid, size of feet, and length of leg in 
the wild, parent species, in pouters, fantails, runts, barbs, 
dragons, carriers, and tumblers. Now some of these birds 
when mature differ in so extraordinary a manner in the 
