EMBKYOGENY 227 



through a Goniatite stage and that frequently the 

 internal convolutions of an Ammonite in their form, 

 ornamentation, and lines of suture * resemble any other 

 earlier existing genus in the adult condition/ 2 That 

 is quite natural. 



It is quite natural, since each alteration, whether 

 retrogressive or progressive, influences the entire indi- 

 vidual. If, for instance, a Sea Lily assumed another 

 form either by specialization or in a definite direction 

 as adaptation to a definite mode of life it would there- 

 fore only reject the hitherto embryonic development 

 in so far as the new complete form to be created rendered 

 necessary. The new constructions would be simply 

 added to the former constructive process, and so it 

 has remained until the present. The newly acquired 

 is always the last in the ontogenesis, the old becomes 

 always the younger or more embryonic. All cases 

 brought forward and really observed thus only show 

 how little since the Palaeozoic period the types like 

 the Sea Urchin, Sea Lily (Crinoids), etc., have changed. 

 The entire transformation indeed is confined, for 

 example, in the Belinuridse mentioned, to those few 

 alterations which in the evolutionary course of the recent 

 Limulus follow upon the Belinuridse stage, precisely 

 as in the case of a retrogressive transformation for 



1 The long since extinct Ammonites (Ammonhorns) were shell-dwelling 

 Cephalopoda which in certain interspaces sometimes constructed a new 

 dwelling chamber in the earlier ones ; the line of separation between each 

 two chambers is called the suture line (division seam). This forms one 

 of the discriminating specific characters and was subject to constant 

 modifications. 



2 Deperet : Umbildung der TierweU, p. 107. 



Q2 



