416 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



oxert a nuitiv.il prossui-e upon one another. Tho deeper parts of tlie layer, arc characterized by 

 tlie presence of patches of tinely granular j)ioinent matter, arranged closely or somewhat distant 

 from one another. In the areas of g-reatest concentration th(» gi-anules extend almost to the 

 Ijcriphory of the ectoderm, l)ut they are mainly internal to the nucleai' zone. Prolialily th(\v are 

 to he regarded as of the nature of pigment granules, and are to l)e distinguished from the granules 

 of glandular cells. They are manifestly the chief cause of the general opacity of the body v all 

 in many tissipai'ous .species. (See also, Ii^ophyllhi^ PI. XVII. fig. 122.) 



jies()(;l(1-:a. 



The mesoglcea" of coral polyps has generally been descritied as a perfectly structureless layer, 

 without any of the migrant coimectivc-tissne cells, such as are characteristic of the mesogkpa of 

 the greater number of Actinian polyps. The homogeneous condition is found in manj' of the 

 .species here descriVted, especially Avhere the polyps are small. Imt in others it becomes somewhat 

 more complex. The layer .stains feebly, or not at all, and when perfectly homogeneous and 

 tran.spai'ent may be indistinguishalile from the clear field of the microscope. 



In large ]>olyp.s. such as Lsopliyllia dipsacea^ and also in JLeandr/'iia, the mesoglcea is rather 

 thick, and minute connective-tissue cells occur sparsely thi'oughout. In sections the cells are 

 circular or oval in shape, with a central nucleus, and minute i)rolongations extend in all direc- 

 tions; many of these I'each one or other of the surfaces of the layer, and there come into con- 

 tact with the ectodermal or endodermal cells. In some instances the proce.s.«ie.s extend right 

 across from on(> layer to the other, but are mostly disposed in an ii'regular stellate manner. 

 Their close connection with the ectoderm and endodcrm would seem to indicate their origin from 

 one or both layers, except in the mesentei'ial mesogkea, where oli\ iously they can ))e deri\(>d 

 oidy from the endodcrm. 



The mesoglcea is usually of uniform charsicter and ci)nsistency throughout any polyp, but a 

 slight difl'erence is revealed in preparations of hophylJin dipmcea, which have been stained with 

 borax carmine and methyl blue. The layer is colored a bright blue, but narrow tube-like por- 

 tion.s, which scarcely take up any coloring matter, stretch across the layer, or in other sections 

 appear as .small, light-colored disks: with ha'matoxylin it remains unstained, and exhibits no such 

 diti'erentiation. 



The ectodermal and endodermal surfaces of the mesogkea are mostly even, but in .some 

 regions, especially on the face of a mesentery which ))ears the longitudinal musculature, the 

 surface 1)ecomes folded, or may even form complicated branching plaitings, so as to afford an 

 increased area for the muscukii- tibrils (PI. XVIII. tig. 130). The endodermal surface in the 

 uppermost region of the colunui may also be deeply folded for the same purpose (PI. XVII. 

 tig. L21). In no case, however, has the musculature 1)een found to become actually end)cddc(l 

 within the mcsogki-a of the cohunn. such as occurs among anemones where a strong mesogkcal 

 sphincter is formed {Sagurtldiv). 



As the me.sogkca is practically alike in sti'uctui(> throughout the tissues of any polyj). it will 

 bi^ unnecessary again to refer to it in dt^tail in describing the individual organs. Along the line 

 •of attachment of the mesenteries to i\w skeletotrophic tissues, and less frequently elsewhere, 

 peculiar mesogkcal processes occui' which scimu to serve as a means of attachment of the ])olypal 

 tissues to the skeleton (PI. XIII. tig. '.Ti). They an* fully n^ferred to on page 481. 



ENIHJDEKM AND SPHINCTER Ml'SC'LE. 



Gland cells, hotli in the clear and granular condition, ai-e the main constituents of the 

 endoderm. Supporting cells are le.s.s numerou.s than in the ectoderm, while the musculature is 



"111 a preliminary note, "< )n the .Vnatomy of a supposed New Species of Camopsammid from I^ifu," >[r. Stanley 

 <7ar(liner proposes the name "skeleto^'liea" for the structureless lamella or jelly of tlie Actinozoa, instead of a 

 ''makeshift term," such a "luesogloea." The introduction of this new term would undoubtedly lead to great confu- 

 sion if emiiloyed in the literature of skeleton-producing polyps, while such has never been the case with Bourne's 

 term, now universally adopted. "Skeletogliea" would have served aptly for the jelly-like, homogeneous matrix in 

 which theskeleton is laid down (p. 483). In his fuller paper (1900, p. .■!.5S), Cardiner prefers to use the term "struc- 

 .turele.'-s memlirane" or "basement membrane." 



