IN THE EMBKYOGENY OF THE HIGHER ANIMALS. Hi.') 



tliouoli now only as an occasional abnorniallty. But when 

 the breach is yet farther widened by one or more repetitions 

 of the process of gemmation, we have a result so totally un- 

 like the ordinary course of reproduction in the majority of 

 animals, that it is with some difficulty we can realize the 

 existence of any community between them. The case 

 seems to stand thus : Gemmation of the embryonic struc- 

 ture may be said to occur in all cases, though in the higher 

 animals only in a latent form, and without trenchinc; on 

 the unity of the organism ; while multiple gemmation 

 exists in the higher only as a monstrosity, and a repetition 

 of it is wholly unkno-wn. Still as the difference is due to a 

 progressive exaggeration of a feature conmion to all, we 

 must regard it as one rather of degree than of kind, and 

 therefore not such as to interfere wdth a certain essential 

 though hidden community of nature — and this even when 

 we come to apply it to such cases as the series of precur- 

 sory zooids among the Trematode Entozoa. 



This way of viewing the case has a bearing on the ques- 

 tion of " zoological individuality," before referred to, for as 

 we consider the germinal mass and the embryo which suc- 

 ceeds it in the light not of two animals, but of mere suc- 

 cessive stao-es in the existence of one and the same animal, 

 so the whole succession of rudimentary Trematoda or 

 Echlnococci may also, in a certain [embryological] sense, be 

 considered as making up but one animal with the typical 

 Distoma or Toenia in which the series terminates. The 

 separate links of the chain of succession, at all events, have 

 not the same distinctness of organic individuality in cases 

 of alternation, as belongs to the consecutive generations of 

 animals high in the scale of organization, in whose develop- 

 ment the embryonic stage — when the typical conformation 

 begins to take shape — is never broken off from the ger- 

 minal in any similar way. 



