Bd. VI: 4) THE ECHINOIDEA. 8 1 



tion on these plates, being found also in the grown specimens on the second pair 

 of interambulacral plates beyond the periproct. It is thus seen that the fasciole 

 does not alter its relations to the plates, its apparent shifting of position being due 

 to the development of new plates inside it. The same fact holds good for the peri- 

 proct and the »latero-anal« fasciole, as the part of the primary fasciole behind the 

 transverse band should be termed. It is thus not surprising that Professor AGASSIZ 

 was unable to trace »the transfer of the anal opening to the exterior of the fasciole* 

 (vChallenger» Echinoidea p. 181),* the reason being, not that the specimens were 

 too young for showing it, as AGASSIZ supposes, but that it is not transferred at all; 

 it retains its original position within the primary, (not the peripetalous) fasciole. 

 — The latero-anal fasciole soon becomes less prominent and generally wholly dis- 

 appears later on; already in a specimen of 8 mm. length I have found it quite rudi- 

 mentary, but mostly it remains distinct until a size of about 20 mm. length. Some- 

 times it may also be distinct, especially the part below the periproct, in fullgrown 

 specimens. 



Regarding the development of the petals the following facts are to be noticed 

 (Figs. 19 — 22). In the specimens of 4 mm. length (Fig. 19) there are 6 pairs of 

 plates, with double pores, within the fasciole in the frontal ambulacrum. In the an- 

 terior lateral ambulacra 4 — 5 pairs of small plates have appeared inside the fasciole; 

 they are perforated, but only with a single small pore each; those outside the fasciole 

 are not perforated. In the posterior lateral ambulacra there are as yet only the 

 ocular plates seen inside the fasciole. In the odd anterior ambulacrum the further 

 development (Figs. 20 — 22) simply consists in the augmenting of the number of 

 plates and in the plates becoming broader; this is done by growth mainly along the 

 median edge of the plates, as must be concluded from the fact that the pores retain 

 their position near the outer edge of the plates. 



In the anterior lateral ambulacra the pores have become double in a specimen 

 of 5 mm. length, and even in both the anterior and posterior series; on the other 

 hand I find the pores i n the anterior series single as yet in a specimen of 6 mm 

 length. I suppose this difference is due to the sexual difference, the specimens with 

 the earlier development of the pores being probably the females, in which the am- 

 bulacra have to reach a much larger size than the males. At a size of 8 mm. length 

 the anterior ambulacra are already distinctly petaloid, with ca. 6 pairs of pores in 



* In the place quoted Professor Agassiz says: »This fasciole, from its position, must undoubtedly be 

 the peripetalous fasciole, as it agrees in position with the same fasciole in Brissopsis, though in the latter 

 genus it does not enclose the anal opening. In the adult HemiasUr the anal opening is not thus surrounded, 

 an additional example of the little value we can place upon the anal opening as a systematic character.* 

 The evidences of the true morphological value of the primary fasciole given here and in the >Tngolf» Echi- 

 noidea II (p. 111 — 114) [Brisaster fragilis) show the remarks quoted to be erroneous. 



11 — 100133. Schwedischt Sudpolar-Expedition igoi—iqol. 



