50 Cuming s — Development of some Paleozoic Bryozoa. 



The now generally accepted classification of the stages of 

 growth and decline, proposed by Alpheus Hyatt, 13 has never 

 been consistently applied to a colonial organism, such as are the 

 Corals and Bryozoa, nor to one whose ontogeny presents the retro- 

 grade metamorphosis which characterizes the latter class. It 

 must be borne in mind that a colony or stock composed of a num- 

 ber of individuals may be properly characterized as nepionic, 

 while some of the individuals composing it are in reality mature, 

 senile, or even dead. The nomenclature of Hyatt applies solely 

 to an individual developing from an ovum, that is, in the case 

 of the Bryozoa, to the first individual of the colony. It fol- 

 lows, therefore, that before the colony has reached a stage in 

 which its genus or even its family is recognizable, the first 

 zocecium, which the author here proposes to designate as the 

 protwcium* has become mature (ephebic). The colony would 

 thus be phylembryonic,t while the protoecium is ephebic. 

 Probably no confusion would arise from this source, if the exact 

 sense in which these terms are used in a specific case, whether 

 as applying to the individual or to the colony, were distinctly 

 stated. Since the development. of a bud presents ho parallel 

 with the early stages in the development of an individual from 

 an ovum r there can be no confusion of terms up to and includ- 

 ing the typembryo. It will be convenient, therefore, to have 

 for the growth stages of a colony a nomenclature which entirely 

 avoids the confusion attending the use of the terms nepionic, 

 neanic, etc. Hence, the writer would submit the following set 

 of terms, composed of the appropriate age-indicating word, as 

 above, combined with the Greek word aoro (dsty), a town or 

 assemblage of dwellings : thus, nepiasty, neanasty, ephebasty, 

 and gerontasty, meaning an infant, adolescent, mature, or 

 senile colony; and nepiastic, neanastic, ephebastic, and 

 gerontastic, the corresponding adjectives. 



Description of Figures 1-15. 



Figures 1-15. — Development of a Chilostomatous Bryozoan, Schizoporella 

 unicornis. (After Barrois.) 



1. Mesembryo ; 2. Metembryo ; 3-5. Formation of the endoderm:}; ; 6, 7. 

 Intermediate stages in the formation of the free-swimming larva ; 8. Normal 

 larva ; 9. Evagination of the adhesive organ ; 10. Reversal of the mantle ; 

 11-14. Degeneration of the larval organs during the first sedentary stages ; 

 15. First appearance of the polypide stage corresponding to fig. 26. 



c, coronal cells ; bl, blastopore ; end, mes, endoderm ; r, retractile disc ; 

 s, ap, adhesive organ (adhesive plate) ; gl, py, pyriform organ ; r.in, rudi- 

 ment of polypide ; pol, polypide (double vesicle stage of Calvet 5a ). 



All figures x 110. 



* From 7rpd)Toc, first, and bailor, house or abode. \ Jackson. 14 



\ The investigations of Calvet 5a have disproven the views of Barrois 

 regarding the differentiation of the endoderm and mesoderm and the fate of 

 the part marked r.ex in the figures. Nevertheless his figures present the gen- 

 eral course of development with such clearness that it has seemed best to 

 reproduce them and call attention to the points which lack full confirmation. 



