14 THE VOYAGE OF H.M.S. CHALLENGER. 



We have as yet but few data regarding the development of the fascicles. As far as the 

 palseontological development is concerned, we find that the earliest Spatangoids, like the 

 Dysasteridse, have no fascicles. In the Cretaceous period we have at first Spatangoids either 

 with a peripetalous or with a sub-anal fasciole; then we have Spatangoids with both; and 

 finally Spatangoids in which the two are connected by a lateral branch, or in which the branch 

 may form an independent fasciole. We find in Adetes Spatangoids, and in those Spatangoids 

 which have no peripetalous fasciole, that the passage from the petaloid to the apetaloid 

 part of the ambulacra is quite gradual, and that in the older genera the plates of the am- 

 bulacra are of comparatively uniform size from the apex to the actinostome, while in 

 those genera in which the peripetalous fasciole exists we find a marked contrast between 

 the infrapetalous plates and the following ones ; and, owing to the crowding of the addi- 

 tional plates of the petals within this sharply-marked line, we find that the Spatangoids 

 with peripetalous fascioles also have more markedly petaloid ambulacra. It is also 

 within the areas of these fascioles that the ambulacral suckers attain a great development 

 as in Brissojms, in Aempe, in Aceste, in Schizaster, and in the area of the sul>anal 

 fasciole within which the ambulacral pores often take a very regular arrangement forming 

 a sort of shield edged by the fascioles. As Loven has akeady suggested, everything we 

 know of the appearance of the anal fasciole seems to show that the anal, lateral, and 

 marginal fascioles are only modifications of the sub-anal fasciole and of its branches, and 

 that the sub-anal fasciole itself may even have originated as a loop of the peripetalous 

 fasciole, although at present the palseontological evidence renders it somewhat doubtful 

 whether the sub-anal and peripetalous fascioles have not originated independently. The 

 internal fasciole I look upon as being an embryonic peripetalous fasciole.^ There is 

 nothing in the development of the Pluteus to show that the vibratile cords forming such 

 characteristic fascioles in the larvge of Echinoderms have any relation whatever with the 

 fascioles of the full-grown Sea-urchin ; yet every writer who has treated the subject of 

 fascioles invariably goes out of his way to make a comparison between the fascioles and 

 the vibratile cords of the Pluteus ; as the fascioles are developed on plates which, as a 

 rule, have not yet appeared during the existence of the \dbratile cords, it seems difiicult 

 to trace the connection between the two in subsequent stages of growth. 



ACANTHOLOGY. 



In an exceedingly interesting paper - on the Acanthology of the Desmosticha, Mr 

 Mackintosh has proposed a classification of the spines of the Desmosticha which, as far 

 as his sub-series are concerned, agrees weU with the afiinities of the families of the 

 group as generally adopted. The primary series do not present, it seems to me, the 



1 See remarks on Aceste and Aerope. 



2 H. W. Mackintosh, On tbe Acanthology of the Desmosticha, Trans. Roy. Irish Acad., vol. xxvi., 1878. 



