THE APODOTJS HOLOTHUKIANS 57 



backward considerably posterior to the point where the intestine bends for- 

 ward, and, being united together over the left dorsal radius, they form a blind 

 sac which Semper has called the "mesenterial canal."- In Myriotrochus 

 minutus the mesentery is greatly reduced, and there are special connections 

 between the loops of the intestine and with the body-wall. The mesenteries 

 are usually attached a little to one side of the mid-line of the interradius in 

 which they lie. They consist of a very thin layer of connective tissue, with or 

 without muscle fibers and covered on each side with the epithelium of the 

 body-cavity. 



CILIATED FUNNELS. In the body-cavity of all Synaptids, so far as known, 

 except Rhabdomolgus ruber and Labidoplax buskii, there occur minute, more or 

 less funnel- or cornucopia-shaped bodies conspicuously ciliated over a part of 

 their surface (Plate V, figs. 11, 12, 20, 21; Plate VII, figs. 14, 23, 28). These 

 ciliated funnels are very characteristic of the family, and are not known to 

 occur in any other animals. They are very few in number in Leptosynapta 

 minuta and it may be that they will yet be found in the species of Labidoplax 

 and Bhabdomolgus, where they are said to be wanting. They most commonly 

 occur upon the mesenteries close to where the latter join the body-wall, but 

 they may occur on the body-wall itself and on the face of the mesentery also. 

 They may occur in connection with all three sections of the mesentery or only 

 with one or two. The funnels may be individually distinct and uniformly 

 separated, they may occur in small groups, or a number may be united into 

 a cluster having a common stem (Plate VII, fig. 14). They range from less 

 than 80 /A to considerably over a millimeter in length. When connected on 

 a common stalk, the whole group may be nearly a milimeter high, and the 

 individual funnels range from 70 to 250 /*. In any one species the size as 

 well as the arrangement of the funnels is fairly constant, though in some cases 

 two very distinct sorts of funnel occur in the same individual. Thus in Lepto- 

 synapta inhcerens the ordinary funnels are generally less than one-tenth of a 

 millimeter in height, but scattered here and there among them are funnels of a 

 somewhat different shape from four to twelve times as large (Plate V, fig. 

 20). The stalk of the funnels is always a slender strand of connective tissue 

 covered with an epithelium, both direct continuations of the same tissues of 

 the mesentery or body-wall. In groups having a common stalk, the latter is 

 said to contain muscle fibers. The funnel itself is made up of connective tissue 

 covered on the outer (convex) side with the flattened epithelium of the body- 

 cavity and lined with an epithelium of high, cylindrical, crowded cells, each of 

 which bears a cilium. The exact form of the funnel, the thickness of the 

 various parts, and the size of the space inclosed vary greatly in different 

 species, and to some extent in different individuals of the same species, and in 

 different funnels of the same individual. 



