216 A. E. V err ill — New Actinians. 



rower and thinner; those of the second cycle bear smaller 

 gonads, on the upper parts in the storaodeal region. In the 

 larger specimens seven pairs of small imperfect mesenteries 

 intervene between the perfect pairs, there being four hexam- 

 erous cycles. The small mesenteries decrease in breadth suc- 

 cessively ; those of the second and third cycles have well 

 defined thickened, but narrow, muscles ; those of the fourth 

 are very narrow. 



The wall is flexible, but moderately thick and tough, owing 

 to the well developed but irregular mesogloea, which rises 

 internally into irregular lobulate processes, corresponding to 

 the external plications and wrinkles. It becomes thin and soft 

 in the capitulum. The circular muscle is distinct and con- 

 tinuous, but thin. The sphincter in section is elongated, 

 becoming thicker near the upper edge (fig. 30, s). There is a 

 large mesenterial foramen in the stomodeal region (fig. 30, f). 



Family Bunodactidje Ver. See No. II, p. 42. 



The principal distinction of this family, as compared with 

 Paractidce, is the sharply circumscribed endodermal sphincter 

 muscle, which is often only attached to the wall by a part of 

 its outer surface. Its outline, in section, is usually ovate or 

 subcircular, but it varies in form in the same species, accord- 

 ing to the degree of contraction. Many Phyllactidse (Aster- 

 actis) have a similar sphincter, and it is probable that they will 

 hereafter be united with this family. The mesenteries and 

 tentacles may be either hexamerous, decamerous, or octamerous, 

 and are often irregular in number and arrangement.* There 

 are usually two pairs of directives and two siphonoglyphs, but 

 may be only one ; sometimes there are three, or even four. 

 These variations may occur in one species. Perfect pairs of 

 mesenteries are usually 12 or more, and generally all are fertile 

 and strongly muscular. Yerrucse or adhesive suckers are 

 usually present on the column, but not always. E"o acontia 

 are present. 



* As a rule, the anatomical investigations of actinians have, up to this time, 

 beeu based on a single specimen, or else on a very few, usually collected at the 

 same season of the year, so that we do not know whether the gonads do, or do 

 not, develop successively on the different mesenteries, even in common species. 

 Moreover, in several cases where considerable numbers of specimens of one 

 species have been dissected, variations often of the most remarkable kind have 

 been found in the arrangement and number of the mesenteries ; number of pairs 

 of directives, and of perfect mesenteries ; form of the sphincter, etc. This is 

 especially the case in several species of Sagartia, Metridium, Bunodactis, Urticina 

 crassicornis, etc. Of the latter, I have found many specimens hexamerous, both 

 as to tentacles and mesenteries ; many others decamerous ; some octamerous ; 

 and a few irregular or unequally developed on opposite sides. Thus it seems 

 that such internal anatomical characters are often as variable and no more reliable 

 than external characters in certain groups of Actinana. 



