MEM. M. C. Z., IX. Xo. 3. — ACALEriLS, rOLYl'S. ' 47 



10. A young polyp perfectly developej, having two cycles of tentacles. At the base tlic wall (c Ihi:.) limiting the 



cnp of the young pulyp has already become very evident. 



11. The internal (entoderm) and external (ectoderm) layers are sharjily marked. The elongated calcareous 



nodules indicate the points of origin of the septa. The tliree centres of deposit for each septum are 

 located not in the e.\tcrual but in the Internal (eutodermic) layer. (Compare Koch's results, below, 

 figs. lS-28.) 



12-15. Balnnoi>hyllia rcrjia. From E. Jourdan, Eecherehes zoologiques et histologiques sur les Zoanthaires du 

 GoUe de Marseille. Ann. sci. nat., ser. G, zooh, Tom. X., Art. no. 1. PI. XVII. ligs. 123, 121, 12ti, 127. 



12. Vermiform larva, "j. 



13. A more advanced larva. J. 



14. Longitudinal section of a larva of the same stage as the preceding. 



15. Transverse section of a larva having six mesenterial plates, vis d. The mesodenn in process of formation. 'i*. 



16. NuTB. — Figures 16 and 45 have been transposed by the lithographer. For the exjilauation of ligure 16 see 



below. 



45, 17. Aslnea (sp. ?). From A. 0. ICowalevsky, Observations on the development of the Ccelenterata. From 

 the Publications of the Imperial Society of Friends of Natural Sciences, Anthropology, and Ethnography. 

 Moscow: 1S73. (Russian.) Plate V. figs. 15, 17. 



45. Longitudinal section of the large, ciliated, brick-red larva. The central mass {vt.}, evidently deiived from 

 cells, is now composed only of nuclei {nl.) and oil globules [gU. oL). The entoderm {en.) of the present 

 stage forms only a part of the numy-layered entoderm of the fully developed polyp, the balance being de- 

 rived from this central mass. 



Note. — The dotted line from en should not have been carried as far as the central mass, but should 

 have ended in the layer of colunmar cells sepai-ating the ectoderm from the central mass. 



17. View of the lai-va from the oral end after it has become attached and flattened. t(i'. The rudiment of a 



tentacle. The radial or intermesenterial chambers (r. cam.) appear as transparent cavities. 



Note. — The central ends of the mesenteries bounding all the chambers except two are grouped in 

 pairs, and in such a way as to nnike the w hole appear symmetrically divided by the line -q. That this line 

 cannot, however, represent the projection of the plane of bilateral symmetiy, is very evident from the 

 studies of other observers. 



18-28. Asicriiidcs calycnlaris. From 0. von Koch, Ueber die Entwicklung des Knlkskeletes von Asteroides caly- 

 cularis und dessen morphologischer Bedeutung. Jlittheilungeu aus der Zoologischen Station zu Ncapel, 

 Bd. III. 1882. Taf. XX., XXI. 



18. Somewhat more than onedialf of a radial section of a young larva, killed the last of June, which had at- 



tached itself to cork (S). The first trace of the skeleton lies between ectoderm and cork in the form of 

 small, more or less fused, calcai'eous concrements, ex. The section along the floor jiasses longitudinally 

 through the eutodermic thickening (cnK) corresponding to the place snbscipiently occupied by the calca- 

 reous .septa (con)pare figs. Ill and 20, en'., sep.). *^. 



19. Portion of a. section from tlie same individual, parallel to the preceding section, but distant from the centre. 



Three mesenteries (hi n/.) and two of the entodermie thickenings {en'.) are cut transversely. The begin- 

 ning of the skeleton {ex. ) is also to be seen below the ectoderm, ^t^. 



20. Portion of a section similar to the preceding, through an older individual. One mesentery with a median 



layer of connective substance (mesoderm, visd.), Harjked on either side by entoderm, is cut across, as are 

 also two calcareous septa (scp.), continuous with the floor-skeleton. \^. 



21. Marginal portion of a section from an individual killed in the middle of July. To show the formation of 



the epitheca {ex.). ^i^. 



22. A small portion of the base from the section shown in fig. 18, more highly magnified. The entoderm is 



vacuolated and contains nuclei. The mesodermie connective tissue is scarcely discernible (not well rcjiro- 

 dnced in the lithograph). The eetodermic cells are nucleated and have sharp contours, especially at their 

 free ends. The calcareous concietions {ex. ) are very small spheroids and double spheroids which lie between 

 the free ends of the eetodermic cells and the cork. 



23. A portion of the preceding still more magnified, and giving a better idea of the form of the concretions and 



their relations to individual cells. 



24. The cells of the ectoderm from another part of the same section, together with a calcareous concretion. 



25. A stage .somewhat older than that (compare figure 8) in which the septa remain separate. The latter have 



acquired by their lateral outgrowths a complicated form. A portion of them have fused with each other at 

 the periphery to form the first trace of the mural layer («!»?•.); in the centre also several have joined their 

 fellows. A narrow rim of epitheca {ethc.) is already formed, but remains distinct from the nniral layer. 



