4G 



EMBIIYOLOGICAL MOXOGEAPHS. 



PLATE XIII. 



Development of Zoantharia and Alcyonaria con tinned. Fir/nres from Henri de Lacaze- 

 DuTiiiERS, Etienxe Jourdax, a. O. Kowalevsky, G. von Koch, Edmund B. Wilson, 



and R. V. WlLLEMOES-SuilM. 



1-11. Astrnides cnhjcularis. From Lacaze-Dutliiers, Developpement des Coi-alliaires. Deuxieme meraoire. 

 Antiniaires a polyjiiers. Arch, de Zool. e.xp. et gen., Tom. II. 1873. Pis. XIl-XV. 



Note. — Tlie .sei|uence of the stages is indicated by the following order of the figures : 1, 6, 9, 5, 7, 

 2, 3, 4, 10, 11, 8. 



1. A free-swimming larva witli strongly expressed s|iiral form, which it assumes whi'n in motion. The arrow 



indicates the direction of tlie motion, the aboral end being in ailvani'c. 



2. Oral aspect of a larva with 12 mi'senteries. The twelve lobes thus formed are diviiled by the first pair of 



mesenteries, as in Actinia (see- Plate XI. figs. 12-16), into two groups of 7 and 5 ropectively. The order 

 of succession of the mesenteries is the same as for Actinia. 



Note. — It will lie seen by comparison that the Cth and Gth are transposed, as compared with 

 Actinia ! 



3. 0)ilic|uo view of the abornl euil of the same larva. 



4. A more advanced larva than the prec;eding. After having begun, while in the free state, the forniation of 



calcareous nodules in its tissues, it is now attacdied, and tentacles liave made their ajipearance. 



5. The embryo begins to undergo a modification of form. The mouth (or.) is seen at the summit of an eleva- 



tion suiTounded by the peristome ; the foot is relatively reduced in size. 



6. The same larva as seen in figure 1. Granules are seen escaping from the mouth, -which is jilaced .above. 



7. Side view of an embryo whiidi has attached itself to the microsco]iic slide. 



8. View of the base of a specimen in which the calcareous septa are forki'd at their periiiheral ends, the tines 



of the forks being short. The mural (c]iilhecal ?) layer (c Ihc.) is already formed, but the septa are not yet 

 joinetl to it. 



9. All embryr) slightly compressed ; before compression the surface .showed no trace of a striation, altliough the 



walls of the body h;id advanced into the cavity and very young mesenteries were already developed. 

 Tlie distinction bet u ecu tlie inner and outer lavf'is is evident. 



