based on the principle of Cephalization. 325, 
lly in an increased laxness and lengthening of the parts, with 
little increase in the dimensions of the body anterior to the 
mouth; while the abdomen (or posterior extremity) is enlarged 
10 to 50 times beyond the bulk it has in the Crab. Descending 
from a snail to an oyster, there is diminution anteriorly and 
great enlargement posteriorly, and the animal is little more than 
a visceral sac. 
In less marked cases of the amplificative method, there is only 
an attenuation or lengthening of the body and limbs, as in many 
Viewed on the ascending grade, this method is the concentra- 
tive ; and it is exhibited in the increased abbreviation and conden- 
sation of the anterior and posterior members and segments, or of 
the whole structure—For examples, see further volume xxii 
and the present, as already referred to. ; 
6. Multiplicative-—Exhibited in an abnormal multiplication a 
Segments or members; as in Myriapods, Worms, Phyllopods, 
2, Compound multiplicative ; as in the Myriapods of the Iulus 
division, or Diplopods (Chilognaths), in which there is a duplica- 
tion of the pair of legs of a body segment. The name Diplopod, 
adopted by Gervais and some other authors, has the advantage 
of having thus a dynamical value. . : 
he multiplicative method is, in general, a degradational one, 
When it affects only subordinate parts of the structure, as the 
length of the tail of Mammals, or of Reptiles, etc., the forms are 
not necessarily degradational. But when it affects the general 
Structure, and the t are indefinite in segments, like the 
yriapods, Worms, and Snakes (see page 4 of this volume), the 
forms are degradational. In Mammals, the tail may be said to 
have indefiniteness of limit; but, since this part is only an 
appendage to the body and has little functional importance, its 
elongation cannot properly be regarded as a mark of degrada- 
tion, although one of inferiority. When, however, the posterior 
extremity is, in magnitude and importance, a part of the main 
body structure itself, as in Snakes and Fishes, the case is prop- 
sug oe example of multiplicative degradation. ee 
| abnormal number of segments under the multiplicative 
