The remainder of the body of Actinotrocha corresponds with the trunk of Balanoglossus. Its body-cavity is distinct from that of the collar, and is divided by a ventral mesentery, though not by a dorsal mesentery. A noteworthy fact is that both Actinotrocha and Tornaria swim by means of a ring of strong cilia or membranellae[52] which surrounds the anus. {29}[Illustration: FIG. 14.—_Actinotrocha_-larva of _Phoronis_. _a_, Anus; _b.c^1_, _b.c^2_, _b.c^3_, first, second and third body-cavities; _c_, circular nerve, running in the posterior boundary of the collar, immediately behind the ring of tentacles; _c.r_, ciliated ring; _d_, diverticulum (paired) of alimentary canal; _m_, mouth; _n.s_, central nervous system; _p_, nerve running round the ventral border of the proboscis; _s_, sense-organ; _s.s_, subneural sinus, a vascular space whose hind wall is constituted by the front boundary of _b.c^2_, its front wall being formed by the hind wall of _b.c^1_; in this region is seen a median outgrowth of the alimentary canal, which may be compared with the notochord of _Cephalodiscus_, or of the young Tornaria (cf. Morgan, _J. Morphol_. v. 1891, Plate xxvi. Fig. 40.) (After Masterman.)] Important memoirs on the structure of Actinotrocha have recently been published by Ikeda,[53] de Selys Longchamps,[54] Goodrich,[55] and Schultz,[56] who criticise many of Masterman's statements. While it is admitted on all sides that an oblique septum following the line of the bases of the tentacles completely subdivides the body-cavity, Masterman's account of the anterior cavities is not confirmed, the spaces indicated by _b.c^1_ and _b.c^2_ in Fig. 14 being stated to be really continuous with one another, while the "subneural sinus" (_s.s_) is regarded as a part of this space. It appears, however, from the account given by Ikeda, and followed by Goodrich, that the old Actinotrocha has two distinct spaces in front of the septum. The first of these corresponds with _b.c^1_ + most of _b.c^2_ in Fig. 14, and is continuous with the cavities of the larval tentacles. Into it project the blind ends of the larval excretory organs, which, according to Goodrich, bear numerous "solenocytes" similar to those described by the same author in Amphioxus and in Polychaet worms (Fig. 79, p. 127). The second cavity is a relatively small crescent (not shown in Fig. 14), lying on the anterior face of the septum, {30}the tips of the crescent nearly meeting dorsally, so as to constitute an almost complete ring following the bases of the tentacles, into each of which it gives off a blind outgrowth. At the metamorphosis, the crescentic space becomes the prae-septal body-cavity and the cavities of the tentacles of the adult, the circular blood-vessel of which is formed from the remains of the large prae-septal space of the larva. Schultz, in calling attention to the fact that both _Phoronis_ and its larva have a striking power of regenerating