notes. 473 



is again, perhaps, connected in the same way with the superficial 

 form. 



79 (i. 241). The G-astrulation of the various classes of 

 animals has been far too little studied to enable us thoroughly 

 to summarize the distribution of the various forms within the 

 separate classes. Yet it is already evident that primordial egg- 

 cleavage and the formation of the Archigastrula occur in the 

 lowest classes of each tribe. 



80 (i. 243). The Rhythm of egg-cleavage is by no means as 

 regular as might appear from the four first examples in the five 

 tables. There are, on the contrary, many variations, and not 

 infrequently an entirely irregular and very variable sequence of 

 numbers occurs (especially in discoided cleavage). 



81 (i. 246). Definition of the Type. Cf, Gcgenbaur, 

 " Elements of Comparative Anatomy," 1874, p. 59. 



82 (i. 246). Types and Phyla. According to the prevailing 

 " Type-theory," the types of the animal kingdom are parallel, 

 and entirely independent ; according to my " Gastrasa-theory," 

 on the contrary, they are divergent tribes, connected at the 

 roots ; according to the view of Claus and other opponents, the 

 latter is no essential distinction. 



83 (i. 248). The one-celled condition of Infusoria entirely 

 forbids their morphological comparison with Metazoa. Cf. my 

 article " On the Morphology of Infusoria " (" Jen. Zeitschrift 

 fur Naturwissenschaft " 1873, vol. vii. p. 516-568). 



84 (i. 257). The axes of the Vertebrate outline. Cf. my 

 " Promorphology " (Stereometry of Organisms). — " Grenerelle 

 Morphologie," vol. i. pp. 374-574. " Singly double-outlines " 

 (Dipleura), p. 519. "Bilateral-symmetrical" forms in the fourth 

 signification of the word. 



85 (i. 255). The Primitive Vertebrate Type, as it is repre- 

 sented in Figs. 52-56, is a hypothetic diagram, which is principally 

 founded on the outline of the Amphioxus, but in which the 

 Comparative Anatomy of Ascidia and Appendicularia on the 

 one side, of Cyclostomi and Selachii on the other, is regarded. 

 This diagram is by no means meant to be an " exact figure," but 



