I90I S. S. BUCKMAN — BRACHIOPODA 237 



Starting from stage attained in IX<^ there is again : — 



XII a. Non-plication (gibbous Fimbriate Terebratida ; Fim- 



valves) developing briothyris ; the recent Magel- 



directly into multiplica- laiiiaflavescens;Rhy7ich. spp. 

 tion. 



XIII Dorsal and ventral sul- Didyothyris. 



cation ; and later a sub- 

 sidiary plica developed 

 within the dorsal sulcus. 



XIV Ventral sulcation pro- Epicyrta Eugen?iii (yon 'Qnch.^ 



nounced. 



This rough analysis of these phases of Brachiopod 

 development will show how homoeomorphy may arise. 

 Non-plicate forms may both start towards plication in 

 similar ways. Or starting in dissimilar ways they may 

 become similar (biplicate Terebrahilce and Glossothyris 

 to a certain extent.) This is particularly marked in the 

 RhyiichonellcB ; in one case the mesial fold is developed 

 and the multiplication follows, in the other case this 

 order is reversed ; but obviously after a while the result 

 must be a similarity in form, a multiplicate shell with a 

 mesial fold in both cases. 



In another case, non-plicate forms may take what are 

 independent hues — one series becoming biplicate, the 

 other bilobate ; yet so far as general appearance is con- 

 cerned the shells of the two series may have a very 

 similar aspect — only different in marginal view. 



The introduction of old age features may often bring 

 about resemblance in what were diverse forms ; but the 

 term " old age features " is relative rather than absolute. 

 For by the principle of earlier inheritance, or tachygenesis, 

 what is an old age feature, in species at an earlier period 

 of phylogenetic development, may soon become a youthful 

 feature in those at a later one. Thus, multiplication is an 

 old age feature in some fimbriate forms ; it is not so in 



