MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 591 



become wholly distinct centriilly: groups of two, three, or four chambers, as the case may be, 

 coninumicate and feebly hang together after decalcification. 



The skeletotrophic tissues are strongly developed, and both the ectoderm and endoderm 

 remain broad la3^ers throughout; the mesoglcea, on the other hand, is only determinable as a 

 dividing line between the two. The endoderm is constituted largely of clear gland cells, the 

 nuclei and zooxanthelliB arranged in a more or less distinct marginal zone. Peripherally 

 in the upper region, and throughout the lower region, very deeply-staining, finely granular 

 protoplasmic ditt'erentiations occur (tig. KiO); in the avidity with which they take up stains such 

 as hematoxylin, carmine, etc., and on account of their finely granular structure, they recall nuclei 

 in the early stages of mitosis. They are distributed in the deeper parts of the layer, usually 

 close to the mesoglcea, and sometimes are present in large numliers. 



In the peripheral and lower regions the calicoblast layer remains very broad; in fact, as 

 broad or even broader than the endoderm (fig. 1.57). It has lost all the ordinary characters of a 

 columnar epithelium; cell divisions are not determinable, and the contents are mainly protoplasmic, 

 with numerous very large vacuoles, and small, rounded granules, which stain readily. The 

 granules are often arranged in irregular rows, stretching from the mesoglcea to the free surface, 

 in which latter region they ivre most crowded. Now and again very small ovoid bodies are met 

 with, which readily stain; thej^ appear to be the same as those described liy Bourne as modified 

 nematoblasts. 



In the more central parts of the polyps the calicoblast layei' is somewhat thinner, and nuclei 

 are more numerous, and h<n-e it is found assuming a more columnar character. Deeply-staining 

 desmoidal processes occur, most usually connected with the synapticula (fig. 157), though not limited 

 to this position. The skeletotrophic tissues in both species of Siderca^trxa are exceptional in the 

 slight increase in thickness which the endoderm undergoes from above downward, as well as in 

 the persistence of the calicoblast ectoderm as a broad layer. 



Female gonads were found in many of the polyps sectionized from one colony. The ova occur 

 singly, or two or three together, near the attached end of the mesentery, and are elongated and 

 rather irregular in shape, having to adapt themselves to the very narrow interseptal loculi 

 within which the mesenteries occur. The length of an ovum is often three or four times the 

 breadth. They mu}^ occur on any of the mesenteries of the three orders. 



Family LOPHOSERID^Ti;. 

 Genus AGARICIA Lamarck." 



Polyps smooth, discal and tentacular systems distinct, but columnar boundary indeterminate; 

 arrang-ed in subconcentric groups which are more or less radiately separated; united with one another 

 along: a common thecal edge, which is strong'ly marked concentrically, but usually less so radially; the 

 gastro-coelomic cavity and mesenteries are continued at the margin (edge-zone); forma frondiform or 

 horizontally flattened foliaceous skeleton, with polyps on both sides or only on upper side, fixed by a broad 

 incrusting base. Column wall not overloding on retraction; no sphincter. Tentacles rudimentary or 

 small, tubercular or digitiform, distant from one a.nother, subcyclical, exocoelic wanting. 



Mesenteries irregularly multicyclic, directives wanting; all filamentiferous; increase by irregular 

 intercalation of single unilateral pairs. Septal invaginations entocoelic and exocoelic; irregularly 

 multicyclic. Interseptal loculi perforated above by circular skeletal ingrowths (synapticula). 



Asexual reproduction by complete discal fission ? 



Examples. — AgariciafragUh Dana, ^1. agaricitev (Linn.). 



Vaughau (IVtOl, p. 63) agrees with Gregory in combining the genera Agaricia and. Mycedkmi, 

 and recognizes only the two West Indian species, .1. fntgiliii and ^1. (igaricitt'><. The specific 

 distinctions are, however, very slight, ))ut among living colonies, as with the coralla also, 

 coarser and more delicate forms can always be separated. Structurally I have been unable to 

 detect any important difi'erences l)etweeii the two species. Only ^1. frag'diH will be here 

 described. 



« "Colony foliaceous and irregular in shape. Calices on one or both surfaces, circumscribed or limited at least 

 on two sides, in transverse or concentric .series, which are separated by unequal rid;jes (collines), over which the 

 confluent septo-cost;e pass. Columella tuberculous, pa])illose, or comprecsod, Septa confluent, not numerous. 

 Comraiin plateau striated and nakeil. Synapticula exist." (Duncan, 18S.5, p. IGl.) 



