1883.] in Reptiles , Birds , and Mammals . 635 
prey. The young of almost all European species have a 
brown plumage, marked with black longitudinal dashes 
which sometimes form black lines, and are subsequently 
resolved into longitudinal spots. The females often retain 
this plumage, but sometimes in them — at least in age — it is 
transformed into a transverse pattern. In the male this 
change takes place, as a rule, on the approach of maturity. 
The longitudinal stripes persist longest on the under surface 
of the body. The back loses all pattern, and becomes con- 
colorous, first in the male, whilst transverse stripes may 
remain on the lower side of the tail and the wings, or on 
the entire under surface. Hence the back of these birds is 
the first part to display new properties. Numerous in- 
stances show that here also, as with lizards, the youthful 
design persists longest in the anterior part of the body, 
whilst the new design begins at the posterior extremity and 
spreads headwards. Sometimes all these stages of trans- 
formation may be met with in the plumage of a single bird. 
Thus the throat may have long stripes, the breast longish 
spots, which lower down pass into a broken design of spots 
forming a transition to the transverse pattern, which becomes 
fully pronounced on the tail, whilst the back has become 
concolorous. The “ law of undulatory development” is 
therefore as manifest among birds as among lizards. 
Herr Eimer summarises his observations on falcons as 
follows : — In youth, leaving the earliest down out of consi- 
deration, as it has generally no design at all, we find a 
brown ground-colour and a pattern of longitudinal stripes 
predominate. In the female both these features persist 
longest, whilst new characteristics appear in the males, and 
especially in the elder males. The new features appearing 
are transverse stripes, and a grey, greyish blue, rusty brown 
or black colour. The transverse pattern appears earlier 
than the new colour. Each new stage of pattern appears 
first in the vigorous adult males. The forms with the more 
advanced characters always pass through the lower stages. 
The females of each form remain on a lower stage, and 
generally on the next lower stage than their respective males. 
Finally, it always appears that the new features, especially 
the transverse stripes, commence at the posterior extremity 
and advance forwards, the youthful design persisting longest 
at the head, whilst the upper surface is changed more 
rapidly than the lower. 
Herr Eimer then extends his observations to the Mam- 
malia, summarising his results as follows : — Among the 
mammals, also, the distribution of colour may be reduced 
2 T 2 
