THE RECAPITULATION THEORY 321 



Kleinenberg has recently directed attention to 

 cases in which the larval and adult organs develop 

 independently the larval nervous system for 

 instance, aborting completely and forming no part 

 of that of the adult. I am not sure that I fully 

 understand Kleinenberg's argument, but it seems 

 very possible that such cases, which are probably 

 far more numerous than is yet admitted, may be 

 due to what may be termed the telescoping of 

 ancestral stages oiie within another, which takes 

 place in actual development, and may accord- 

 ingly be grouped under the head of develop- 

 mental convenience. Undue prolongation of an 

 early ancestral stage, as in cases of abrupt meta- 

 morphosis, must involve modification, especially 

 in the muscular and nervous systems; in such 

 cases a telescoping of ancestral stages takes place 

 as we have seen, the adult being developed within 

 the larva. , Such telescoping must distort the re- 

 capitulatofVjjiistory, and as the shape of the larva 

 and adult may differ widely, an independent origin 

 of organs, especially the muscular and nervous 

 systems, may be_acquired secondarily. 



The stage in the development of Squilla, in which 

 the three posterior maxillipedes disappear com- 

 pletely, to reappear at a later stage in a totally 

 different form, is not to be interpreted as meaning 

 that the adult maxillipedes are entirely new struc- 

 tures unconnected historically with those of the larva. 

 Neither is the annual shedding of the antlers 

 of deer to be regarded as the repetition of an an- 

 cestral hornless condition intercalated historically 



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