WHAT IS EVOLVED IN EVOLUTION? 26/ 



thyrium. These we call ordinal characters; the Magellania 

 is of the order Clistenterata, or hinged Brachiopods. 



But these characters have a continuous succession back 

 to the Lower Cambrian. Again, we notice on the smaller 

 valve two plates, called teeth sockets, producing with the 

 outer part of the hinge margin a groove or socket into 

 which the teeth fit, and at the base of them a pair of calci- 

 fied processes, called crura; but these too are traceable back 

 to the Lower Cambrian (Fig. 62). 



Calcified Loops which are Subordinal Characters were Evolved 

 between the Cambrian and Silurian Eras. — The Magellania dif- 

 fers from some hinged Brachiopods in having, in addition to 

 the crura, calcified bands of a peculiar form looped back 

 upon themselves, which are technically called loops. These 

 are characters of a part of the hinged Bracliiopods, and they 

 are called subordinal characters, separating the suborder An- 

 cylobrachia from all other suborders of Brachiopods. But 

 these loops cannot be traced backward further than the base 

 of the Silurian; they are not known in the Ordovician or Cam- 

 brian. Regarding the characters of the specimen of as high 

 as class and ordinal rank, we have no evidence regarding their 

 origin save the law of hereditary transmission by ordinary 

 generation ; but Magellania has loops which it could not have 

 gotten by the law of heredity, i.e; considered as a law of the 

 transmission of like characters from ancestry to progeny. If 

 we assume that the law of hereditary descent vs^ill satisfac- 

 torily explain the reappearance on successive organisms of a 

 character which has once been formed, then we have the ex- 

 planation of the class and ordinal characters of such a speci- 

 men as far back as to the Lower Cambrian, but its subordi- 

 nal characters can by this means be accounted for only back 

 to the Silurian. In other words, we are led by this train 

 of reasoning to the conclusion that this Magellania had 

 ancestors which did not possess its subordinal characters, 

 among which are the calcified loop of a particular shape. 



Each Case of Evolution a Case of the Appearance in some Indi- 

 vidual of a Character not possessed by its Ancestors. — In the same 

 way we learn from embryology, or the ontogenetic growth of 



