576 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



proximal rciiioii, hut occiirts more distally. iuul ;m octodoi-iual musculature is strongly developed. 

 The eiidoderm eoutaiiis few zooxautlieli;e. 



The peripheral ectoderm of the disk presents a wide contrast from that of tlie more central 

 area. The latter very closely resembles the outer layer of the colunui wall. Iteiiig opa(jue 

 throughout, with the j>ranular matter strongly developed; at tlie periphery, however, the 

 ectodermal cells are longer, a larger number of clear gland cells are present, and little granulai' 

 matter occurs. A few nematocysts may also bo pr(>sent, but apparently no ectodermal muscidature 

 is developed. The mesogltfa is a little thinner than in thecolunm wall, and its endt)dermal asjicct 

 is plaited for the support of the musculature, most niarived in the peripheral region. 



Ti-ansvei-se sections of the stomodanun display strong vertical ridges opposite the insertion 

 of the mesenteries, while the intervening areas are much thinner; large oval nematocysts occur 

 in the ectoderm of the ridges, but are absent from the grooves, which in their turn are more 

 strongly ciliated. The ridges and furrows thus present somewhat the same histological diti'er- 

 ences which exist between the general ectoderm and the gonidial grooves in Actinians. The 

 granular pigmentation chai-acteristic of the ectoderm of the column wall is absent from the 

 stomodival ectoderm; the mesogkea is everywhere thin, and only a weak endodermal nnisculatur(> 

 is developed. 



The mesenteries are without any regular cyclic arrangement, and no directives occur. The 

 greater number of the pairs arc complete, but alternating incomplete pairs are also present in 

 places, the ditlerent pairs varying in size. The incomplete members are evidently recently 

 developed pairs which in time will become complete. 



The mesoghea on the mesenterial face bearing the retractf)r muscles is wavj' in transverse 

 sections, or forms numerous plaits, which, however, vary greatly in the extent of their develop- 

 ment, both in dilierent mesenteries and in different regions of the same mesentery-. In the 

 middle region of some of the mesenteries both mesogkeal faces are sinuous for some distance, and 

 the oblique muscidature on the opposite face is strongly developed. The mesenterial epithelium 

 is narrow above, but becomes verj' broad below, and consists mainly of clear gland cells; 

 zooxanthellre are also pi-esent. In the lower region most of the mesenteries become much 

 con\'oluted, and nearly till the septal loculi. Mesenterial filaments are borne on all the mesenteries, 

 whether complete or incomplete; the mesenterial endpderm behind is swollen in some instances 

 and not in others. Clear gland cells are somewhat numerous in the upper course, and in the 

 lower are many large oval nematocysts. In some cases the hlament has undergone complete 

 glandular modification, and the areas stand out very prominently in sections, as the contents of 

 the gland cells are a deep yellow. The modification is limited to the filament, without involving 

 the endoderm behind. 



The skeletotrophic tissues are characterized by the great thickness of the endoderm in the 

 lower regions, and by its almost complete vacuolization. Actual cell outlines have altogether 

 disappeared, and the few protoplasmic contents are aggregated in a narrow marginal zone. The 

 calicoblast layer is broad in some regions; numerous desmoidal processes occur along the 

 course of the insertion of the mesenteries, and here the mesogloea is nuxch broadened. 



The septal invaginations are only entoc<£lic, and do not encroach much upon the gasti"o- 

 ccelomic cavity until neat- the aboral end of the polyp, but even here the interseptal chambers 

 are not distinct from one another. 



Female gonads were present on some of the mesenteries, restricted in their distribution 

 toward the insertion of the mesentery in the body wall. Generally onh' three or four ova are 

 seen in a transverse section of any mesentery, and may occur on either the complete or 

 incomplete mesenteries. 



