I I 



of the anlerior cdge of the collar in ihat aiiimal. In olhcr wiM'tls, the opercuhim must be taken 

 into account, as indeed I formerly suofgested (87, p. 46), although in Cephalodiscus this region 

 has not been spHt uj) into arms or tentacles. In constructing a diagram to shew the actual 

 anatomical relations of the arms and opercuhun in Cephalodiscus, I arrived at the result seen 

 in hg-. 159. This diagram is supposed to represent an individual in which the proboscis was 

 directed forwards (as in fig. 23), the proboscis itself having been cut away with the exxeption 

 of the part which is present in the proboscis-stalk. The operculum is further supposed to have 

 been stretched so as to pass completely externally to the series of arms, instead of being 

 partially concealed by their bases in the way shewn, in a dorsal view, in fig. 158. The free 

 anterior edge of the collar thus forms a funnel leading to the mouth, incomplete dorsally, and 

 elongated in a transverse direction, the lateral parts being reflected towards the dorsal side. 

 This diagram, constructed without any theoretical bias, has considerable resemblances to figures 

 of the lophophore of Phoronis, for instance to those given by Benham (89, PI. X, figs. 12, 7). 

 It is indeed possible that the interruption, in the mid-dorsal line, of the series of tentacles 

 described by Benham and other authors in Plioronis may be related to the fact that the free 

 edge of the collar is interrupted in a similar position in Cephalodiscus. It may be noted, in this 

 connexion, that Schultz (03, i, p. 405), in describing the regeneration of the lophophore in 

 Phoronis, calls attention to a bifid condition of that structure which he specially compares 

 with the two lophophoral arms of Rhabdopleura. 



De Selys Longchamps (04, p. 38) gives a description of the vascular system ol Phoronis 

 differing in certain respects from that of most of his predecessors. It appears from his statements, 

 confirming an earlier account by Schxeider, that both the principal longitudinal vessels of the 

 adult are differentiated on the dorsal side of the stomach of the larva, from a space which 

 originates between the splanchnic mesoblast and the epithelium of the stomach, and (pp. 89 — 91) 

 that they communicate with one another merely through a splanchnic sinus which has the same 

 relations. It is perhaps significant, in this conne.xion, that the largest vessel in Cephalodiscus 

 is the dorsal vessel (figs. 22, 33, 37; rt'. f.) ; that this vessel appears to originate from the wall of 

 the stomach as a space between the splanchnic mesoderm and the digestive epithelium 

 (figs. 57, 58); and that the only communication between the dorsal vessel and the posterior 

 vessel of the stalk seems to be through a splanchnic or gastric sinus similar to that of Phoi'onis. 



In his account of the muscular system de Selys Longchamps (04, pp. 108, 115) discusses 

 the supposed predominance of that of the protocoele or proboscis-cavity in Masterman's group 

 Archichorda, and he comes to the conclusion that Phoronis does not shew this predominance. 

 I may be permitted to point out that Cephalodiscus shews it no more than does Phoronis. 

 The principal musculature of the former is assuredly the great mass of muscles in the stalk 

 and on the antero-ventral side of the metasome. This is equally the case in Phoronis, in which 

 (p. 115) "Ie tronc est la région musculaire par excellence". 



With regard to the nervous system, and leaving on one side the description, which has 

 not been confirmed by later authors, given by Mastermax (97, i) of the peripheral nervous 

 system of Actinotrocha, it may be noted that the nervous system of Phoronis remains in the 

 epidermis, externally to the basement-membrane, and that there is evidence (de Selys Longchamps, 



