13Jr C. E. Beecher — Development of the Brachiopoda, 



of a larval form doubtfully referred to Discinisca. The results 

 of these observers must at present be taken without reserva- 

 tion, and are thus made use of in the present paper. 



Something is known, therefore, of the earty stages in each 

 of the four groups or orders proposed by the writer. 1 The 

 Atremata, Neotremata, and Protremata are represented by a 

 single genus only in each ; Glottidia, Discinisca, and Lacazella, 

 respectively ; and the Telotremata, by Cistella, Terebratulina, 

 and Lioth} r rina. Were Glottidia and Discinisca as well known 

 as Cistella, Terebratulina, and Lacazella, some comparisons 

 could undoubtedly be made which would enlighten many ob- 

 scure points of anatomy and morphology, as well as give 

 clearer insight into the history and origin of each group. 



Cistella and Terebratulina are taken as standards of the 

 embryological development on account of the completeness 

 with which they have been studied, and because their points 

 of difference are not great. Lacazella shows such peculiar 

 features, that its history must be discussed separately. The 

 nepionic Glottidia and Discinisca, too, present characters 

 which evidently had an early history somewhat different from 

 Cistella or Terebratulina. 



In taking up the review of the observed stages of growth, 

 an attempt will be made to fix their limitations. To this end 

 the admirable nomenclature proposed by Hyatt 9 ' 10 is here 

 adojjted, as it is more convenient and of wider application and 

 significance than the terms heretofore used. Thus far this 

 system has been employed principally in studies relating to the 

 mollusca, and its application to the Brachiopoda will neces- 

 sarily require some illustration and explanation. In the 

 preface to " Genesis of the Arietidae," Hyatt has presented a 

 summary of the theoretical opinions resulting mainly from his 

 studies in the Cephalopoda, It is believed that nearly the 

 same ground may be covered in the Brachiopoda, and thus the 

 truth of these deductions will receive further evidence from 

 another class of organisms. 



Embryonic stages. 



The true embryonic stages are classified by Hyatt as Prot- 

 embryo, Mesembryo, Metembryo, JVeoembryo, and Typembryo. 

 To these Jackson 11 has added the Phylembryo, taking it from 

 the later stages of the Typembryo to represent the period 

 when the animal can be referred definitely to the class to 

 which it belongs. 



The succeeding stages in the growth of the animal to 

 maturity are termed by Hyatt nepionic (young), nealogic 

 (adolescent), and ephebolic (mature), while old age characters 



