ME. P. H, CAEPENTER ON THE GENUS ACTINOMETEA. 79 



larger tliau the iuterradial coelom (i/). It is also seen in Taf. xv. figs. 25, 20, on a larger 

 scale ; and in Taf. xiv. figs. 20-24 both the radial and the interradial diverticula of the 

 body-cavity are seen in transverse section, separate from one another towards the dorsal 

 side, but communicating freely nearer the ventral surface, both with one another and 

 with the centre of the plexus. In figs. 20-2-1!, Ludwig has accidentally lettered them 

 U and U' respectively. This is unfortunate, as these letters are employed by him in 

 his other figures to designate the circuuivisceral and axial body-cavity ; while in fig. 26 

 he uses the same letter L to designate the system of plexiform spaces occupying the 

 central funnel of the pentagonal base, as he employs in his other figures for the inter- 

 visceral division of the body-cavity. 



This hardly agrees with his text ; for on p. 43 he says : — " Ueber den ersten Eadialien 

 lost sich die axiale Leibeshohle in eine Summe von mit einander allseitis," commuuiciren- 

 den Maschen riiumen auf, welche zwischen die ersten Radialien eindringen, hier das 

 dorsale Organ [/. e. axial prolongation] umgeben und endlich mit zelm blindgeschlos- 

 senen Fortsetzungen endigen, von denen fiinf radiar gerichtet sind (i^'), fiinf interradiiir 

 {Li). Der Dorsalcanal [=coeliac canal] dcs Armes giebt seine Lage dicht iiber den 

 Kalkgliedern und zwischen und iiber deren Muskelpaaren nicht auf bis er iiber dem 

 ersten Hadiale angekommeu ist, wo er sich gleichfalls in die schon erwiihnten Maschen- 

 I'aume auflost. Letztere stehen also in Verbindung mit der axialen Leibeshohle und mit 

 den Dorsalcaniilen der Arme, aber sie dehnen sich auch ferner nach oben und seitlich aus, 

 und erfiillen hier den Raum der rings um die axiale Leibeshohle zwischen dem Ventral- 

 canal und dem Dorsalcanal in der radiaren Halfte, zwischen Ventralperistom und Dorsal- 

 peristom in der interradiaren Halfte der Scheibe iibrig bleibt." This space, the general 

 perivisceral cavity, falls naturally, as Ludwig has pointed out, into two divisions — one 

 external or circumvisceral, between the visceral mass and the body-wall, and corresponding 

 to the " coelom " of Dr. Carpenter ; and one internal or intervisceral, surrounding the axial 

 body-cavity (or axial canal of Dr. Carpenter), and occupying the spaces between the 

 various coils of the alimentary canal within the visceral mass. This last corresponds 

 to the intramural spaces and mesenteric sinuses of Dr. Carpenter ', and not to the former 

 only, as Ludwig appears to think (p. 55). 



Of all the divisions of the body-cavity this intervisceral coelom is the one which is 

 least directly connected with the plexiform network between the first radials (Ludwig, 

 figs. 26, 74, L) and with the coeliac canals of the arms ; for it is completely separated from 

 the latter by the visceral layer of the peritoneum, except at the minute aperture in the 

 under surface of the visceral mass, where the axial prolongation, coming up from the quin- 

 quclocular organ through the central vacuity of the pentagonal base, enters the inter- 

 visceral coelom contained within the visceral mass. When the latter is turned out of 

 the calyx the intervisceral coelom contained within it is, of course, removed at the same 

 time, while the plexiform system of spaces between the first radials, and the continuations 

 of the cceliac canals of the arms which terminate in it, are laid open ; both of these, there- 

 fore, are manifestly portions of the general c/rcwwvisceral cavity surrounding the visceral 

 mass. Ludwig, however, makes the following statement (p. 90) : — " Die Ilauptab- 



' Proc. E. S. uo. IGG, 1S7C, pp. 216, 217, 225. 



