26 Coelenterata. 



In the macrocnemes the trilobed portion of the filament extends much further 

 down the mesentery, the single-lobed part being limited to its terminal part, 

 which is almost straight. The filament throughout its trilobed portion, except 

 in its uppermost part, may give rise to craspedonemes, but the different species 

 vary in the extent and distribution of these structures. In C. membr. and 

 americ. they occur in considerable numbers, in the form of long threads on 

 the edges of the mesenteries, a short distance below the stomodaeum; in P. fimbr. 

 they are few in number and comparatively short and digitiform, but they are 

 present at intervals along the entire length of the trilobed portion of the fila- 

 ments of the macrocnemes. In the filaments of P. fimbr. there is a median 

 streak, and two distal and two proximal lateral ones. The median one is com- 

 posed chiefly of narrow, elongate, ciliated cells among which are a few gland 

 cells but no nematocysts, basally there are a few muscle fibres and a nerve 

 layer. The distal lateral streaks are composed of gland- and nematocyst- 

 cells, the proximal lateral streaks contain slender, strongly ciliated cells, but 

 not gland- or nematocyst-cells. In C. americ. the structure of the filaments is 

 essentially the same, but the median streak is broader and the muscles better 

 developed. The craspedonemes are folds of the edge of the mesentery over 

 which the filament passes. In P. fimbr. they are broad and low and the as- 

 cending and descending limbs are separated by a broad band of endoderm. In 

 a section of a craspedoneme of a macrocneme the median and two pairs of lateral 

 streaks are distinguishable; but in a section of a brachycneme, or in one from 

 near the terminal portion of a macrocneme, the median streak is much reduced 

 or absent. In C. americ. the endoderm separating the limbs of the craspedo- 

 cnemes is much reduced, giving a quadrilateral appearance in section. The 

 structure of the simple portion of a mesenterial filament is similar to that of 

 the distal lateral streaks above described, numerous nematocyst- and gland- 

 cells being present. Acontia have not been found in adult specimens. The 

 trilobed portion of the mesenterial filament arises apparently from the stomo- 

 dseal ectoderm, at any rate as far as the lateral streaks are concerned, but 

 the evidence regarding the lower single-lobed portion of the filament is imper- 

 fect. The author adopts the following classification of the Cerianthese - - sub- 

 order Acontiferse (van Beneden) in which the 2d or 4th, or both, protocnemes 

 bear acontia, at least during the early stages of development; the deuterocnemic 

 tentacles appear in the same order as the mesenteries to which they correspond. 



(1) Cerianthidse, the telocnemes are the 2d couple of protocnemes, the suc- 

 ceeding protocnemes are represented by a brachycnemic couple (usually sterile) 

 and by a macrocnemic couple; acontia, in the larval stages, upon the telo- 

 cnemes and, in some cases, upon the macrocuemic protocnemes - - Ceritmthw, 

 the following species are described - - ambonensis (all the mesenteries, except 

 the directives, fertile, hermaphrodite, ova and sperms occurring on the same 

 mesentery), sulcatus, tcedus n. (hermaphrodite; none of the mesenteries, not 

 even the telocnemes, extend to the aboral pole or its vicinity, mesenteries 

 alternately sterile and fertile). Larval forms Apiactis I n., Peponactis 1 n. 



(2) Arachnactidse , the telocnemes are the 4th couple, the 2d and 3d couples of 

 protocnemes are sterile, acontia in the larval stages upon the 4th protocneme, 

 never on the 2d - - Pachycerianthus, species described - - fimbriatus (n. nom.), 

 monostichus (n.). Larval forms Arachnactis 1 n., Dactylactis 1 n. 



Me Murrich( 1 ) states that in Arachnactis albida and sibogcB n. the length of 

 the tentacles is many times the diameter of the disc, in A. bournei and bra- 

 chiolata the tentacles are about as long as the diameter of the disc. In sib., 

 as in alb., the median marginal tentacle appears only after the formation of 



