eo ey ee eo a a ee Foe 
Botany and Zoology. 311 
irregularity of time of appearance of the different characters of 
animals during their period of growth, as affecting their permanent 
structure. While maintaining the view that the low forms repre- 
sent the eer ge stages of the higher, he proceeds to account 
for the want of exact correspondence exhibited by them at the 
present time, on reference to this principle. He believes — the 
relation of parent and descendant has been concealed and changed 
by subsequent modifications of the order and appearance of charac- 
pe in growth. To the original simple —" he es the 
mm palingenesis ; to the modified and later growth, ¢ 78. 
The causes of the change from palingenesis = emnogencs “ne re- 
gards as three, viz: acceleration, retardation, and heter 
It is clear that sat: two types of growth distinguished wt Prof, 
Heckel are thos which had been pointed out by Prof. poet in 
“The Origin of Rice ra,” as producing the relations of “exact 
and “j Catan parallelism ; ;” and that his explanation of the origin 
of the latter relation by acceleration or retardation is the same as 
that of the latter essay. The importance which he attaches to 
the subject was a source of gratification to the speaker, as it was 
a similar i el orens that led to the publication of “The Origin of 
Genera” in 1869. 
or onemcae are pies as necessarily accounted for 
time. Hence it may be laid do own, that synchronous a 
tion or retardation produces exact parallelism, and ha or ce 
ration or retardation produces inexact parallelism. 
four types which the segmentation now prese 
rat = oo of the laws of evolution may . tabulated as fol- 
Exact repetition. 
Acceleration, which proceeds ms) Modified repetition. 
Heterotopy. 
dation, whi Exact atrophy. 
ea which proceeds by Tieiaget aeohy (or senility),* 
and each of the methods may be either of Exact par eat the 
dele of Palingenseis, which is synchronous ; or Inexact para al- 
ct of 0 i 0 ite 
* So called by ‘Booka + Hyatt. 
