ee ee ete eal 
le 
1883.] The Polar Organization of Animals. 489 
mately interwoven outgrowths. In the interspaces of these or- 
gans other matter is deposited, which serves for their support and 
forms the connective tissues. 
Such is the true character of the mesoderm. The wall of the 
inner cavity becomes the digestive region of the body. It differ- 
entiates accordingly, involutions of it compose the various glands 
which aid digestion, and blood vessels which have their true ori- 
gin in its walls, carry the nutriment which it yields to all parts of 
the interior. So the outer wall becomes the sensory layer of the 
body, and sends its nerve channels inwards to convey motor en- 
ergy to muscles, which are, fundamentally, but special arrange- 
ments of nerve extremities. The mesoderm consists of these 
Sutwardly-pushing nutritive and inwardly-pushing motor channels, 
i the connective tissues necessary for their support. The 
‘femaining general function of the body, that of the elimination of 
aste and discarded material, is effected through the aid of both 
layers, 
So far we discover in the highest animal only a direct unfoldment 
of What exists in the lowest. Protoplasm may be homogeneous 
in structure, and every portion of it at once sensitive to external 
contact and assimilative of nutritive material. But the different 
relations of its different regions necessitates an early differentia- 
‘ton of function. It becomes externally sensory, internally nutri- 
tive. And in the highest animals this differentiation continues. 
{tis remarkably unfolded, but there is nothing added to it. Its 
ous vagueness, however, becomes a marked specialization. 
We find in the simplest protozoan a double polarity vaguely de- 
clared. The first is a chemical or sexual polarity, in which the 
two lateral halves of the mass are concerned, and whose eventual 
A result is the division of the mass into two vitalized halves. The 
second is a sensory-nutritive polarity, of which the external and 
— internal r egions of the bod 
Be Sige y mass become the poles. Both these 
polarities 
are direct results of the native conditions of protoplasm 
relations to external nature. And in the highest animals 
nothing more than an extension of these differentiations 
Polar; atities n and function, and a more specialized display of these 
The sexual polarity seems to still affect the two oppo- 
and its 
‘prec... -S!0NS, so that every animal, except as warped by the 
‘Pressure o 
f life conditions, is symmetrically duplex, the two simi- 
~~ Peang, as we believe, the male and female poles of a 
