BROOKS AND RITTENHOUSE : ON TURRITOPSIS. 459 



8. The formation of the endoderm follows none of the typical 

 methods described by Metschnikoff. It arises late in the larval life 

 from the svncvtial mass of tissue left in the interior of the embryo 



V V 



after the separation of the ectoderm by the mesogloea. When the 

 cells first reappear they are crowded together without any definite 

 arrangement; finally they come to form the distinct endodermal 

 layer. 



9. During the late segmentation there is evidence that some of the 

 nuclei divide amitotically. 



10. The planula becomes attached on the side by nearly its entire 

 length, and is transformed into a root. 



O } 



11. The first hydranth develops from a bud which is given off at 

 about the middle of the root soon after attachment. 



12. The tentacles develop in indefinite whorls. Each whorl has 

 four tentacles. The oldest are nearest the distal end. In the fully 

 developed hydranth they have the appearance of being scattered 

 rather than of being arranged in circles. 



LITERATURE. 



Brooks W. K. 



'83. Notes on the medusae of Beaufort, N. C. Studies from biol. lab. 



Johns Hopkins univ., vol. 2, p. 465-475. 

 '84. On the life history of Eutima, and on radial and bilateral symmetry 



in hydroids. Zool. anz., vol. 7, p. 709-711. 

 '86. The life history of the Hydromedusae. A discussion of the origin 



of the Medusae and the significance of metagenesis. Mem. Boston 



soc. nat. hist,, vol. 3, p. 359-430, pi. 37-44. 

 Bunting, M. 



'94. The origin of the sex-cells in the Hydractinia and Podocoryne; 



and the development of Hydractinia. Journ. morph., vol. 9, p. 203- 



236, pi. 1-3. 

 Gerd. W. 



'92. Zur frage liber die keimblatterbildung bei den hydromedusen. 



Zool. anz., vol. 15, p. 312-316, pi. 28, 5 figs. 

 Hargitt, C. W. 



'00. A contribution to the natural history and development of Pennnriu 



tiarella McCr. Amer. nat.. vol. 34. p. 387-415, 4 pis., 2 figs. 

 '04a. The early development of Pennaria tiarella McCr. Arch, f . ent \vick- 



lungsmech. d. organ., vol. 18, p. 453-488, pi. 24-28. 



