Embryology. 119 



find. Take, for example, the case of the highest 

 organism, Man. Like that of all other organisms, 

 unicellular or multicellular, his development starts 

 from the nucleus of a single cell. Again, like that 

 of all the Metazoa and Metaphyta, his development 

 starts from the specially elaborated nucleus of an 

 egg-cell, or a nucleus which has been formed by 

 the fusion of a male with a female element 1 . When 

 his animality becomes established, he exhibits the 

 fundamental anatomical qualities which characterize 

 such lowly animals as polyps and jelly-fish. And 

 even when he is marked off as a Vertebrate, it cannot 

 be said whether he is to be a fish, a reptile, a bird, 

 or a beast. Later on it becomes evident that he is 

 to be a Mammal ; but not till later still can it be said 

 to which order of mammals he belongs. 



Here, however, we must guard against an error which 

 is frequently met with in popular expositions of this 

 subject. It is not true that the embryonic phases 

 in the development of a higher form always resemble 

 so many adult stages of lower forms. This may or 

 may not be the case ; but what always is the case 



1 It has already been stated that both parthenogenesis and gemmation 

 are ultimately derived from sexual reproduction. It may now be added, 

 on the other hand, that the earlier stages of parthenogenesis have been 

 observed to occur sporadically in all sub-kingdoms of the Metazoa, 

 including the Vertebrata, and even the highest class, Mammalia. These 

 earlier stages consist in spontaneous segmentations of the ovum; so 

 that even if a virgin has ever conceived and borne a son, and even if 

 such a fact in the human species has been unique, still it would not be- 

 token any breach of physiological continuity. Indeed, according to 

 Weismann's not improbable hypothesis touching the physiological 

 meaning of polar bodies, such a fact need betoken nothing more than 

 a slight disturbance of the complex machinery of ovulation, on account 

 of which the ovum failed to eliminate from its substance an almost 

 inconceivably minute portion of its nucleus. 



