242 Colonial Organisms. (March, 
to cause a nearly complete unfoldment of the original life plan. 
The main difference between the larva and the Annelid segment, 
or the Hydrozoan organ, is, that in the former the animal is 
checked in an embryonic stage, in which it possesses full life 
functions; in the latter it attains its mature stage, but with only 
a portion of the life functions. In the former it displays an inde- 
pendent immaturity, in the latter a subordinated maturity. But 
with these distinctions we seem to behold in all these phenomena 
the results of one law of nature, a checked development, under 
the force of circumstances, of forms which have an innate ten- 
dency to complete their development, which tendency becomes 
effective as soon as the retarding conditions are removed, and at ) 
times seemingly in spite of them. There appears to be a pers 
tent strife between the active external conditions and the innit 
hereditary life energies. 
The embryological development of the Annelids presents indi- 
cations like those of the Hydrozoa. They leave the egg as glob- | 
ular masses of untransformed cells. This cell mass elongate | 
and becomes segmented, while the head organs appear anteriori} i 
The number of segments increases by the interposition of new 
ones, the segmental organs appear, and the young am or ; 
the mature form. In this process the indication óf a orl iy 
colonial origin is evident, though perhaps less so than in the mli 
drozoa. The asexual budding by which the mature e ofis 
formed is certainly significant, and points to the 
phylogenetic derivation. : opment 1 
In the Arthropoda appears the highest known deve dk 
this principle of the formation of individuals by the at et 
tion of colonies, Of these the Myriopoda alone presen iit 
indications of colonization, In them the segments are 3 
space. It lacks only the mouth and the senge 
head-segment to be a complete animal. And its 
the indefinite budding of new segments is sig 
origin. of 
In the Crustacéa, Insecta and Arachnida, the ee 
original colonial condition are much less evident, thov A 
ordinarily quite manifest in Crustacean and insect 
organs y 
formation Á 
nificant of 
he | 
