FROM MONER TO MAN. 579 



clei make their appearance. It undoubtedly contains a larger propor- 

 tion of the nitrogenous matter which enters into the composition of all 

 protoplasm, and, like the nuclei of other cells, a certain percentage of 

 phosphorus. At this stage of its existence the germ (still microscopic) 

 is represented in the zoological scale by the Amoeba, which it closely 

 resembles in structure, having thus ascended to the second round of 

 the zoological ladder. 



The amoeba has received its full share of attention from biologists. 

 Its physiological endowments are scarcely greater than those of the 

 non-nucleated moner. Both are capable of effecting those exchanges 

 of matter which constitute nutrition ; both are capable of reproduction 

 (a phase of nutrition) ; both have the power of changing their form 

 by thrusting out portions of their mass (the so called " false-feet "), and 

 of thus executing slight creeping movements. These little masses of 

 protoplasm are also capable of responding to contact of other matter, 

 thus exhibiting the rudiments of common sensation. What is the evi- 

 dence of this capacity ? How does the amoeba manifest a sense of 

 touch ? When some substance, perhaps a smaller representative of its 

 own species, floats against the surface of an amoeba, the precocious bit 

 of protoplasm responds to the salute by flowing around its victim, 

 which is thereby inclosed within the body of its captor, and gradually 

 appropriated as food. Probably the term " victim " is of doubtful ap- 

 plication in this case, since the difference between eating and being 

 eaten must be trifling. However that may be, the one improvises a 

 stomach for the occasion, and digests the other with all the nonchalance 

 of a Feejee-Islander. The human germ is, however, preserved from a 

 similar indulgence in incipient cannibalism by its different environ- 

 ment not the only period of its existence when it escapes evil-doing 

 through lack of opportunity for it receives its pabulum, ready pre- 

 pared, from the blood of the mother, which is doubtless one of the 

 conditions of its future higher development. 



In this response to contact by movement on the part of the amoeba, 

 it exhibits the rudiments of both muscular and nervous action, since, 

 under the influence of an external force or stimulus, a reflex move- 

 ment is produced. 



The next perceptible change in the evolution of the ovum is known 

 as segmentation. This consists in an increase of its mass by duplica- 

 tion and reduplication ; the single cell first acquires a second nucleus, 

 and the surrounding protoplasm then separates into two masses, each 

 having its own nucleus ; this process is continued until the enveloping 

 membrane contains a mass of cells, each like the original amoeboid 

 cell. From the resemblance of the ovum at this period to a mulberry, 

 this is called the mulberry or morula stage of embryonic development. 

 In the zoological scale, it corresponds to the labyrinthida, a little ani- 

 mal which consists of an aggregation of simple nucleated cells. From 

 this multiplication of nuclei, which are regarded as the active centers 



