Hyatt.] 404 [Nov. 16, 



not been found to be true among fossil Cephalopoda, and there 

 exist, so far as known to the author, but few characteristics prob- 

 ably originating in the early stages. The constant recurrence of 

 hereditary characteristics in silphologic and nealogic stages which 

 originated in adults, like those given above for the Endoceratidye, 

 makes the probability of the assumption, that the asiphonula and 

 veliger represent the adult stages of lost types, so highly probable, 

 that the burden of proof must rest upon the opponents of this ar- 

 gument. Each case of the origin of characters in embryos and 

 larvae should in other words be regarded with distrust until 

 proven. 



The appearance of the incomplete modes of segmentation in ex- 

 isting Sepioidea may possibly be a case of origination in embryo. 

 There are no adult forms known to the author, which store up 

 food in their tissues in such a manner that they can be used to 

 explain the origin of the specialized food yolk. Nevertheless 

 special inquiry might have very unexpected results. The case 

 above given of the calcareous nature of the protoconch, and all the 

 other characters of this stage in the Ammonoids and Belemnoids, 

 seemed to have originated in embryo until it was found that a dis- 

 tinct silphologic stage, the asiphonula, existed in Nautiloids, and 

 that this indicated the former existence of an asiphonulate ancestor 

 having a calcareous shell. 



Some of the characters of the goniatitinula, such as the deep 

 ventral saddle of the first septum in the angustisellate young, as 

 described by Branco, doubtless originated in the younger stages. 

 These are, however, correlative with the anarcestian form of this 

 stage and with a general tendency to closer involution, which acted 

 the same way in every series of forms, whether we select series of 

 adults or of embryos for comparison. 



The use of a distinct term for the adult period becomes necessary 

 not onl} r on this account, and to separate its relations from those 

 of preceding periods, but also because of the constant recurrence 

 and importance of representative forms. The term Ephebology 15 

 has accordingly been adopted for the designation of the relations of 

 the adult stages, and under this term can be classified also the rep- 

 resentation of similar forms in different groups or morphological 

 equivalents. These are often so exact that it becomes very diffi- 



^'e^ij/So?, the age of puberty. 



