July, 1891. 
ANIMAL PEDIGREES. 
149 
The capitalist, on the other hand, is enabled, like Hylodes, to 
omit these earlier stages, and, after a brief period of incuba¬ 
tion, to start business with large factories equipped with the 
most recent appliances, and with a complete staff of work¬ 
people, i.e., to spring into existence fully fledged. 
There is no doubt that abundance of food yolk is a 
direct and very frequent cause of the omission of ancestral 
stages from individual development; but it must not be 
viewed as a sole cause. It is quite impossible that any animal, 
except perhaps in the lowest zoological groups, should repeat 
all the ancestral stages in the history of the race; the limits 
of time available for individual development will not permit 
this. There is a tendency in all animals towards condensa¬ 
tion of the ancestral history, towards striking a direct path 
from the egg to the adult. 
This tendency is best marked in the higher, the more 
complicated members of a group, i.e., in those which have a 
longer and more tortuous pedigree; and although greatly 
strengthened by the presence of food yolk in the egg, is 
apparently not due to this in the first instance. 
Thus the simpler forms of Orbitolites, as 0. tenuissima, 
repeat in their development all the stages leading from a 
spiral to a discoidal shell; but in the more complicated species, 
as Dr. Carpenter has pointed out, there is a tendency towards 
precocious development of the adult characters, the earlier 
stages being hurried over in a modified form ; while in the 
most complex examples, as in 0. complanata , the earlier 
spiral stages may be entirely omitted, the shell acquiring 
almost from its earliest commencement the discoidal mode 
of growth. There is no question here of relative abundance 
of food yolk, but merely of early or precocious appearance 
of adult characters. 
Of causes other than food yolk, or only indirectly con¬ 
nected with it, which tend to falsify the ancestral history, 
many are now known, but time will only permit me to notice 
the more important. These are distortion, whether in time 
or space; sudden or violent metamorphosis; a series of 
modifications, due chiefly to mechanical causes, and which 
may be spoken of as developmental conveniences; the impor¬ 
tant question of variability in development; and finally the 
great problem of degeneration. 
Concerning distortion in time, all embryologists have 
noticed the tendency to anticipation or precocious develop¬ 
ment of characters which really belong to a later stage in the 
pedigree. The early attainment of the discoidal form in the 
shell of Orbitolites complanata is a case in point; and Wiirten- 
