Canon A. M. Norman on Cacumaria Montagui. 357 



dermis. This is a difference known to me from the 

 study of the old and young in other species. 



2nd. It is a known fact that spicula found in the young of 

 certain species (e. g. G.frondosa) entirely disappear 

 in tlie adult, or a spicule of another form takes its 

 place. 



3rd. Spicules whicli are entirely free from nodulation in 

 some young Cucumarians become highly nodulous or 

 greatly incrasaated in old examples. I will take as 

 an instance a species I have already referred to, 

 C. Hyndmanni. The plate-spicules as figured by 

 Bell, pi. ii. fig. 1 a, and also a at bottom of the 

 plate, show from two to sixteen perforations and are 

 scarcely thickened. I should not have been able to 

 say positively that tiiese spicula belonged to G. Hynd- 

 manni had it not been for the peculiarly characteristic 

 foot-spicules ; for the plates of the old specimens are 

 often all extraordinarily massive, their thickness being 

 subequal to the breadth ; yet other specimens I have, 

 especially a young one, which have spiculation corre- 

 sponding with BelPs figures. 



4th. The ventral ambulacra in both A and B bear closely- 

 set double rows of feet ; dorsal ambulacra with few 

 irregularly arranged papillce or feet. Thus some 

 authors would place the species in the subgenus 

 Colochirus. 



To sum up my views as regards B and C : I am of opinion 

 that the figures I give, fig. 6 a, b, /, g, h, i, k, represent the 

 primary spicules of the young scattered at depths in the 

 dermis, which will at a later stage be absorbed; while c, d, 

 and e represent some of the earliest spicules developed of 

 those winch will at a later stage constitute the dermal 

 layer. 



I may add that I have studied the spiculation of the Holo- 

 thuroidea for at least forty years ; that I have mountings of 

 spicula (often many mountings) of almost all European 

 shallow-water species and some abyssal forms ; and that 

 while recognizing spiculation as the truest guide to the 

 determination of species, I know full well that allowance should 

 be made for variations in respect of individuals and also in 

 regard to age ; and that on these points tliere remains a 

 valuable field for study. 



After the foregoing was actually printed I happened to 

 turn to E. von Marcnzeller, ' Resultats Camp, scient. Prince 



