KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 25. N:() 2. 43 



of the inner portion, since from it fine lines are seen to radiate to the circumference, 

 indicating a radially plexiform disposition of the stereom. In the outer portion of the 

 ossiele similar tine lines run more parallel to one another, and at right angles to the 

 axial canal; these lines pass across the suture line a short distance into the inner portion 

 of the ossiele, an appearance preoisely similar to that of a elose suture in a recent Cri- 

 noid: the faint transverse ridges of stereom are very much closer together in the neigh- 

 huurhood of the axial canal: these two fäets indicate that a region near and parallel to 

 the axial canal is the centre of calcincation of this portion. The two centres of caleifica- 

 tion are therefore just where one would expect theni to be on any hypothesis of derivation 

 from a round ossiele. The disposition of the stereom seems to indicate that the shape of 

 the ossiele was arrived at by an outward growth laterally, and not by an inward pressure 

 along the median line of the inner curve. Had this latter been the case, the lines that 

 now racliate would have tended to converge. It seems moreover to follow from this that 

 the modineation in the shape of the ossiele was due, not to successive inheritances of a 

 deformation caused by coiling, but to the repeated seleetion of those iudividuals in which 

 the stem more naturall}' lent itself to coiling. This is a kind of evidence not often ob- 

 tainable, and it seems worthy the attention of Neo-Lamarckians. 



Turning now to the outside of one of these ossicles, we can easily distinguish the 

 two longitudinal sutures, which lie one on either side of the square-shaped outer ridge 

 (tigs. 30, 32, 41, 42, 43, 53). Beside these sutures, however, there are seen, in one spe- 

 cies at least (H. JlabfilUcirrUs), three other sutures. Two of these are elose together in the 

 middle of the outer surface (tigs. 63, (>')); the third, which is less obvious, is in the 

 middle of the inner surface, i. e., in the concavity between the two cirri (tigs. 66, 68). 

 The two outer median sutures and the two latera] sutures are all shown in Halls figures 

 of Myelodactyhis cotwolutus {"/>. citt, IT. 42, tig. 6 b, d, c), while there also appear traces 

 of the median inner suture (tig. 6 a). 



Returning to the transections of the ossicles, we can now perceive that two of the 

 inner ridges that pass to the outer curve, at right angles to the axial canal, are split by 

 a suture line (Text-tig. 12 (5)); and in some speeimens the matrix filling the axial canal 

 nia) r be seen to run up into the suture lines. A transection through a rather more distal 

 ossiele shows a similar extension or process of the axial canal towards the inner curve 

 (Text-tig. 12 (6)). The axial canal is in fäet 5-rayed, but two of the rays are greatly 

 extended and enlarged. 



In the more proximal regions of the stem there are, as is always the ease, fewer 

 traces of primitive struetures. A transection in regions 1 or 2 shows the following 

 points (Text-tig. 12 (2, 3, 4)), — a circular or elliptic section; an axial canal, transverse 

 and divided into two lateral canals by a median growth of stereom; very faint traces of 

 the two outer lateral sutures; slight traces of greater muscularity in the portion between 

 these sutures. It would appear from the very peculiar division of the axial canal that 

 the bilateral syminetry of the stem has affected even the interna! organs. 



From the struetures above described it may be inferred that the stem of the an- 

 cestral Herpetocrinus (Text-fig. 12 (7)) was divided by 5 longitudinal sutures into 5 equal 

 parts; that the axial canal was 5-rayed; that the stereom grew out from it in a radiating 



