Fig. 12. 



The Structure of the Stera of Herpetocrinus. 



1. Part of the roiled steni of H. Fletcheri from Wenlock Limestone of Dudley (Brit. Mus. E 295). The black 

 linc is that along wliieh the microscopc-sections were taken after the specimen liad been drawn. a denotes 

 the stem-region from whicli drawing 2 was taken, b that from which drawing 3 was taken, and c that from 

 which drawing 4 was taken. This drawing is natural size. 



2. Transeetion of stem-region 1 in specimen K 295. The large dark mäss in the upper hall' of the drawing 

 probably represents the remains of muscular or ligaraentous tissue concentratod in thal träet. The meaning 

 of the two dark patches in the lower left-hand part of the drawing is uncertain ; perhaps traces of sutnral 

 ligament. It is hardly probable that they are the remains of the axial canal, though it is true that that struc- 

 ture is not otherwise represented in tlie section. 



3. Transeetion of stem-region 2 in specimen E 295. This shows a clear differentation into a smaller upper half, 

 containing traces of muscular or ligamentous tissue, and a larger lower portion, containing the axial canal. 

 These two portions are separated by the lateral sutures, which. however, can hardly be distinguished in this 

 region of the stem. A radiate disposition of the reticulate stereom is ven faintly observable in the smaller 

 portion, but is plainly seen in the larger portion; it is, however, to be noted that the radii are arranged 

 according to a different plan in the two portions. The axial canal is clearly divided, bnt its two halves are 

 somewhat irregular. 



4. Transeetion of stem-region 3 in specimen E 295. The different character of the two portions of the section 

 is very apparent in this drawing, and here the radiation of the stereom is more clearly seen in the smaller 

 portion. In the larger portion the two halves of the axial canal are very distinct. 



5. Transeetion of a columnal from stem-region 5 of H. Fletcheri (Brit. Mus. 57435 a). See full description at 

 bottom of ]>. 42 and third paragraph on p. 43. s denotes lateral suture, and <; cirrus-articulation. The small 

 figure on the left gives the natural size of the object. 



6. Transeetion of a columnal from stem-region G of //. Ammonis (?). The section being slightly oblique, the 

 canals to the cirri are only visible towards the centre of the section. The lateral sutures (s), the large muscular 

 spaces, and the tive rays of the axial canal. are all plainly seen. The small figure on the right gives the 

 natural size of the object. 



7. A diagram giving a hvpothetical restoration of the ancestral stem. s = suture, andc = cirrus. This represents 

 the view put forward in the text. It is, however, possible that the outer median sutures and outer lateral 



