44 FEN ipher—American Trotting Horse. 
Such a change as this connected with the reproductive 
periods is unparalleled, so faras I know, among the Inverte- 
brata, and even among the Vertebrata ; the cases of partia 
atrophy of the generative organs or shedding of antlers (as in 
the stag) after the rut is over are hardly comparable. 
At the time I had the specimens alive my attention had not 
been drawn to the questions relating to the two forms of the 
males, so that I failed to make anatomical examination, and. 
the specimens have now lain too long in alcohol to be service- 
able for internal dissection. JI hope, however, that perp 
who are more —— situated will be able to throw mo 
light on this subject. 
I will add that the males es extraordinary size which I have 
seen, are all of the “first for Do these very old scitbvichinti 
cease to moult? Do they Gaccnie permanently capable of re- 
production ? 
Museum of Comparative Zodlogy, Cambridge, Mass., Nov. 12, 1883. 
ArT. [X.—Hvolution of the American ated Horse; by 
Francis EK. Nip 
In the November number of this Journal, Mr. W. H. Picker- 
ing has criticised the method of reduction used in my paper in 
the July number, and has reached a conclusion very Y didtereah 
from my own. I wish to discuss his criticisms briefly. 
Mr. Pickering thinks it objectionable to determine the value 
of aT ot the change in speed per year, by taking alternate dif- 
‘reid in s and T, and he has reduced the observations by 
taking the differenoes between consecutive values in the table. 
In this way he gets the values in the third column in the table 
below. 
$ Year. —_ obs. | ee calc | E 
= | dT 
vege fe 
141 1861-0 aoe to —01 
131 1869-0 0-46 0-51 -or4 
135 1872°6 as ton +04 
151 aaa : 0-75 0-44 +1°8 
