526 MEMOIRS OF THE NATIONAL ACADEIMY OF SCIENCES. 



Agarieia and IsophyJUa. In the later larv;e of Lebrunia the central part of the vacuolated tissue 

 had heeomo broken down, and cell debris and zooxanthelhe were seen to escape througli the oral 

 aperture; and thus tlie adult ctelenteron was produced, though for a long time the parietal and 

 mesenterial endoderm remained greatly thickened. 



Api)ellr>f, toward the close of liis paper, "' Studien iiber Actinen-Entwicklung." discusses my 

 conception that the endoderm of tiie larva of Lehranla is for a time nuiltilaminar, and concludes 

 that I am mistaken in my interpretation of the appearances. He surmises that Lebrunia is 

 exceptional in that its larval endoderm cells are greatly elongated and highly vacuolated, not that 

 they represent a parenchymatous mass, as my observations imply. The various coral larva3 here 

 investigated show that the more or less solid condition is by no means exceptional in the Zoantharia, 

 but is I'ather the rule. The question at issue is whether the appearances presented l)y sections 

 are due to the vacuolization of a comparatively few elongated cells, or whether the endodermal 

 tissue at this stage is composed of numerous rounded or polygonal cells forming an embryonic 

 parenchymatous mass. 



In whatever direction sections are taken the appearances are the same, the tissue seeming 

 constituted of rounded or polygonal elements; there is never a radiating appearance, such as would 

 be expected did the cells represent a columnar epithelium. The absence of this can not be set 

 down to the disappearance of cell limitations, for such are everywhere very obvious. Moreover, 

 so far as can be judged, each vacuolated element is provided with a weli-detined nucleus, adherent 

 to the wall. 



It is manifest, from all the stages available, that the central portion of the tissue becomes 

 disorganized shortly after the larva's extrusion, when functional activity of the stomodreum has 

 been established. As seen in sections, the middle of the larva at this stage is filled with granules 

 of various kinds, some staining deeply and others colorless; zooxanthelliB and fragments of what 

 seem to be cell walls are also plentiful. Were all the cells fixed to the mesogloea by their l)ase, 

 we should then have to assume that their centripetal ends ])ecome disintegrated and theflebris 

 extruded, a proceeding which would hardly be expected to occur. 



LARVA OF AGAKICIA AGARICITES. 

 (PI. XXV, figs. 165-167.) 



A colony of Agarieia, freshly collected, extruded numbers of larvae within a few hours, all of 

 which were directly preserved. The specimens were opaque and about 3 mm. in length; some 

 were strongly peai'-shaped, and others nearly sjiherical. and all swam about from the ))eginning. 

 So far as could be made out by examination of the living specimens under the microscojje, 

 no oial aperture was yet established; a few zooxanthelhe were present in the ectoderm ai-ound the 

 oral extr^'mity. Most of the larva- partly collapsed on preservation, whether in formalin or 

 corrosive acetic. 



Sections reveal that the larvte are all at the same stage of development. The interior is 

 filled with a compact vacuolar tissue, leaving practically no free cavity, and six pairs of mesenteries 

 are developed, ail of which extend nearly the full length of the ituier cavity; four pairs of the 

 mesenteries are united with the stomodteum throughout its length, but the other two pairs nowhere 

 reach it. Mesenterial filaments are already borne by all the six pairs of mesenteries, and become 

 strongly developed toward the iiboral extremity of the larva. Both transverse and longitudinal 

 sections indicate that the oral aperture is not yet formed, though evidently just about to be so; 

 the stomodreal tube already shows a definite lumen, but at its outer extremity the ectoderm 

 cells still close over it, and would prevent any comnuuiication between the interior and the 

 exterior. No ciliation of the storaodieal ectoderm can be made out, though this character is 

 always very manifest in weil-preserved examples of the adult polyps. That the cilia in this 

 instance have not disappeared, owing to imperfect preservation, may be inferred from the fact 

 that the external ciliation of the ectoderm is still clearly shown. 



The outer ectoderm of the larva is a very broad layer, and the usual histological elements 

 of the adult are already present, comprising supporting cells, gland cells, and nematocysts, 

 with the addition toward the aljoral extremity of a well-developed nerve layer. Zooxanthellse 



