98 ZOOPHYTES. 



system cannot exist, but if muscular fibre be added, the nervous may 

 receive its different degrees of developement. 



There is abundant reason, therefore, in their constitution, for the 

 larger number of ovules in the inferior animals ; for, from their 

 nature, they can concentrate only a small amount of reproductive 

 force on any centre ; and, as the cellular tissue produces myriads of 

 hairs, so animals of this composition may produce immense numbers 

 of small ovules. Add muscular and nervous tissue, and the animal 

 system may concentrate a much larger amount of force and nutriment, 

 proceeding from a wider sphere of action. 



As the species among the inferior grades diminish in size, there is 

 also a consequent decrease — the general constitution being the same 

 — in the number of germs they produce ; and, in the simple monad, 

 vi'e appear to have a single isolated sphere of reproduction, producing 

 its single germ: the texture is mostly cellular tissue, and the size 

 must be just that required to give vital force enough for a single 

 germ; for when this animal enlarges, by nutriment received, so as to 

 exceed its normal size, there is a tendency at once to form two 

 centres ; and, as enlargement goes on, subdivision actually takes 

 place, and two animals are formed of the one. The enlarged size 

 produces more vital force than can belong to a single animal so con- 

 stituted.* In larger animals, of similar constitution with the monad, 

 the number of ovules produced is very large, for the reason, that the 

 animal can concentrate on any single cellule only a small amount of 

 vital force, and, as there is a large amount present, the germs must 

 be numerous. As we ascend in the scale of being, the number of 

 young diminishes. 



In the higher species, where a large nervous system is to result 

 from the germinant cellule, the force required is greater than when 

 this cellule is the germ of an inferior species, with an imperfect 

 nervous system. The physical structure of tlie animal must there- 

 fore be larger to produce the vital power needed for the elaborations 

 that originate the germinant cellule of an animal of the higher 

 grades. Size is, therefore, an important element in the system of 

 organic life. 



96. Although the question is complicated by many circumstances 



* The relation between the number of germs and size is still farther illustrated by the 

 visceral lamellse in difTerent species of Astrceas, as exhibited in the closing paragi-aph 

 of § 43 b. 



