50 THE STORY OF ANIMAL LIFE 



Two things must be noticed before we leave 

 the subject of the Protozoa. One is, that some 

 forms present the beginning of a multiceliular 

 condition. Several units sometimes join together, 

 and in this way a complex object may be formed, 

 in which there are several nuclei ; or the original 

 unit may keep on growing till it consists of many 

 successive portions, and in some of them a fresh 

 nucleus may arise. This occurs in some of the 

 Foraminifera. 



The next thing to be noticed is, that there are 

 a number of organisms which constitute a debate- 

 able ground, and are claimed now by the botanist, 

 and now by the zoologist. While the latter 

 insists on calling them Protozoa (Primitive Ani- 

 mals) the former would have them Protophyta 

 (Primitive Plants). The fact is that in these 

 organisms of the first grade, the distinction be- 

 tween "plant" and "animal" has not become a 

 hard and fast line; and the disputed forms may 

 be best described as links between the two. The 

 chemistry of nutrition is probably more to be 

 relied upon as a distinction, than the difference 

 of structure. It is here that the two groups, 

 plants and animals, start upon different roads, 

 and many of the differences in structure must be 

 regarded as the direct result of the fundamental 

 difference in the mode of nutrition. The follow- 

 ing very instructive remarks on the subject are 

 taken from Professor Hertwig's valuable book 

 " The Biological Problem of To-Day,"* pp. in, 



112. 



" The different mode of nutrition of animals 



* " The Biological Problem of To-Day, Preformation or 

 Epigenesis," by Professor O. Hertwig. Translated by P. C. 

 Mitchell. Heinemann, 1896. 



