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THE AMERICAN NATURALIST [Vol. XLVII 



ornamentation. In the specialized genera Acidaspis and 

 Arges, as shown by Beecher, both dorsal eyes and dentic- 

 ulate ornamentations occur in the protaspis. 



In acceleration of development, when skipping of 

 stages occurs, it is not the earliest or embryonic stages 

 that are skipped, but later or postembryonic. Embryonic 

 stages are clung to with striking pertinacity. Stages 

 are often run together or telescoped as expressed by 

 Grabau, s when in a specialized type more than one phase 

 may be represented at a single stage, although such 

 stages are clearly distinct in more primitive types. 



As an outgrowth of Professor Hyatt's studies of 

 stages in development, the principle of colonial develop- 

 ment has been enunciated independently by Ruedemann 9 

 in Graptolites, by Cumings 10 in Bryozoa and by Lang 11 

 also in Bryozoa. These investigators show that in the 

 growth of the colony there are distinct stages in develop- 

 ment which can be correlated with the adult characters 

 of more primitive colonial forms. In this respect the 

 colony behaves as an individual. Cumings introduces 

 the terms nepiastic, neanastic, ephebastic, gerontastic as 

 descriptive adjectives of these colonial stages. It is 

 felt that this special nomenclature for colonial stages is 

 unnecessary and therefore undesirable, because the 

 simpler the terminology can be kept in such work, the 

 more likely it is to be widely accepted and made use of. 



Another phase of stages is localized stages in develop- 

 ment in which I 12 showed that throughout the life of the 

 individual stages may be found in localized parts which 



8 A. W. Grahau. "Studies of Gastropoda. III. On Orthogenetic Varia- 



»R, Ruedemann, "Growth and ' Development of Goniograptus thureaui 

 M'Coy," Bull. N. T. State Mus., No. 52, 1902. 



R. Ruedemann, "Graptolites of New York." Pt. 1, Mem. N. T. State 

 Mus., No. 7, 1904. Pt. 2, idem, No. 11, 1904. 



10 E. R. Cumings, "Development of Some Paleozoic Bryozoa," Amer. 



U W. D. Lang, "The Jurassic Form of the 'Genera' Stomatopora and 

 Troboscina," Geol. Ma;,., dec 5. Vol. 1, 1904. 



11 R. T. Jackson, "Localized Stages in Development in Plants and Ani- 

 mals," Mem. Boston Soc. Nat. Hist., Vol. 5, 1899. 



