﻿SPONGES.-HALLMANN. j-^ 



■ ance. The smooth oxeofes are asymmetrical, and ivJtcn 

 they attain in the fullest degree their characteristic shape 

 are tornotoxea icith a slight flexion at the tip of the 

 oxeote extremity. The extremes of the maximum dimen- 

 sions of the spicules in the known varieties are as fol- 

 loivs : — Tornotoxea : Letigth, i6o to 220 ]i; diameter, 4.5 

 to 6 ji. Echinating acanthostylcs : Length, 145 to 200 

 fi : diameter, 8 to 12 y. Dermal ac antho style s : Length, 

 So to 100 \i: diameter, 5 to S /i. Isochelw arcnatce : 

 Length, 16 to 2^ \i. 



The several sponges now to be described agree so closely in 

 the form and dimensions of their spicules that^ — despite con- 

 siderable differences in some other respects — it has been con- 

 sidered preferable to treat them as varieties of a single species. 

 Any differences that there may be in the shapes of the spicules 

 in the different varieties are too slight to be of diagnostic 

 value, and a single description will therefore sufTice for all. 

 The megascleres are smooth oxeotes, and acanthostyles of 

 two kinds ; the microscleres are isochelae arcuatae of a single 

 kind. The oxea are slender, asymmetrical, slightly fusiform 

 straight spicules which in their very earliest stages of growth 

 appear to be monactinal. Their characteristic peculiarity — 

 which is usually, however, to be observed only in small pro- 

 portion of them — is a slight bending to one side of the tip of 

 one extremit}. This peculiarity as it appears when most 

 highly de\eloped, is illustrated in text-tigure 29, where it is also 

 to be obser\ed that the spicule is most correctly described as 

 a tornotoxea. Throughout the descriptions they will be re- 

 ferred to merely as the oxea, or sometimes as the auxiliary 

 spicules. The extent to which they enter into the formation 

 of the Hbre-core varies greatly in the different varieties ; in the 

 variety digitata they are pretty well the sole constituents; in 

 the varieties perramosa and levis they are mingled with a 

 variable proportion of acanthostyles ; in the varieties arenacea 

 and rubra they are usually more or less completely supplanted 

 bv acanthostyles. An interesting condition is found in the 

 variety pumila, where columns of oxea, descending down- 

 wards from the surface without admixture of acanthostyles, 

 form a common and characteristic feature of the skeleton. 

 The oxea also occur as interstitial spicules, but except in the 

 variety digitata are outnumbered as such by the accessory 

 acanthostyles ; in the last named variety also, they participate 

 in the formation of the dermal skeleton. The acanthostyles, 

 as pre\ iously mentioned, are of two kinds. Those which 

 predominate as echinating spicules and often in addition core 

 the fibres are straight conical spicules of variable length, pro- 

 vided with more or less recurved spines which are usually 



