336 SEA-SIDE STUDIES. 



we observe one intensely significant fact, namely, that 

 the germ-cell spontaneously passes through the same 

 early phases of its development, ivhether it he fertil- 

 ised or not. The germ-cell of a bird or mammal cannot 

 continue its development, as the germ-cells of Polypes, 

 Entomostraca, Bees, and Moths continue theirs ; but 

 neither is there any fixed limit to its arrest. Some ova 

 fall short at one stage, others at others, but at no stage 

 of theu^ history can we say. Here the aid of fertilisation 

 begins. Every ovum, therefore, of the highest animal 

 as of the loivest, haswithi^i it the power of development 

 unaided by the spermatozoon ; this development falls 

 very short indeed of an embryo, in the highest animals, 

 but it travels some miles on the road towards that goal ; 

 and when, as in insects, the goal is not very distant, it 

 may be reached. We may liken the spermatozoa to 

 the extra pair of horses put to the carriage to enable it 

 to reach a certain distance over mountainous ground. 

 Two horses have dragged the carriage to the foot of the 

 hill, and have brought it by precisely the same route as 

 the four horses would have taken ; but here, at the foot 

 of the hill, the extra horses are indispensable. In grant- 

 ing the indispensable nature of the aid of such extra 

 horses, no one would think of saying that it proved 

 the necessity of foiu- horses to carriage travelling. 



The various modes of Rej^roduction we have seen to 

 be identical, since not only are Fission and Gemmation 

 admitted to be identical, but we have further seen that 

 between Gemmation and Generation no real vital dis- 

 tinction exists. By a real and vital distinction, I mean 



