21 i 



ment '<t' the mesenterial filaments of th.it form, and .1 record of the results, combfned with 

 some observations on the filaments of C. americanus, seems advisable for the purpose ol 

 rounding out our present information concerning the mesenterial filaments of the Ceriantheae, 



In both the forms mentioned all the mesenteries, with the exception of the directivi 



provided with mesenterial filaments, and all of these possess the same histological structure. 



Vs in the filaments of the Actiniaceae, two portions are recognizable in each filament, an upper 



trilobed |>i.rtioii and a lower simpler portion, but in the Ceriantheae marked differences in the 



iment of the two portions are shown by the macrocnemes and brachyenemes. 



In the latter the uppermöst portion immediately succeeding the lower border of the stomato- 



an lias an almost straight free border, and throughout this stretch the filament is trilobed. 



> portion is succeeded l>v a stretch in which the border is much folded and apparently 



branched, and throughout which the filament is single-lobed (this portion is represented as 



wavy in text-figure II, p. [2); and below this again, the free edge is almost straight and the 



single-lobed portion of the filament is continued along it almost to its termination, only the 



terminal portion of the mesentery being destitute of a filament. 



In the macrocnemes, on the other hand, the trilobed portion of the filament extends a 

 much greater distance down the mesentery, as shown by the cross marks in text-figure II. the 

 single-lobed portion being limited to its terminal part, which is almost straight and in no case 

 thrown into the complicated folds and branchings seen in the brachyenemes. 



The filament throughout its trilobed portion, except in its uppermöst part, may give 

 rise to craspedonemes, but considerable differences occur in the different species in the extent 

 of the development and distribution of these structures. In C. memèranaceus and C. americanus 

 they occur in considerable numbers and in the form of long slender threads upon the edges 

 of the mesenteries a short distance below the lower border of the stomatodaïum, and are quite 

 conspicuous in individuals of these species opened under water so that the craspedonemes may 

 float freely. In /'. fimöriatus y on the other hand, they are quite inconspicuous, being few in 

 number and having the form of comparatively short digitiform processes rather than elongated 

 threads. but they are to be found at intervals along the entire length of the trilobed portion 

 of the filaments of the macrocnemes, a condition which does not obtain in C. americanus, 

 although apparently present in C. memèranaceus. 



The minuter structure of the filaments of /'. fimbriatus in the trilobed portion is as 

 follows. The mesogloea of the edge of the mesentery is enlarged into a somewhat quadrate 

 mass (PI. I. I ig. 12 . whose distal angles are produced into slender processes projecting at right 

 angles to the plane of the mesentery. while the proximal angles are prolonged into stouter 

 recurved | ». ( >ver this <pi.idi-.ite mass the epithelium is arranged, and il is differentiated 



into five distinct areas, tour of which are paired, while the fifth, which lines the distal face oi 

 the quadrate thickening of mesogloea, is unpaired. There can be recognized, therefore, in this 

 on of the filament a median streak, two distal lateral and two proximal lateral streaks. 



The median streak Fig. 1 2 M ■ is composed principally of narrow elongated cells, whose 



nu ■ long and narrow. are lo all at about the same level near the distal ends ol the 



uticle lines the free surfaces of the reik. which are provided with strong cilia. 



