REPORT ON THE HEXACTINELLIDA. 187 



spicules " occur not only in the interior of the body but also in the superficial dermal 

 layer ; the rays of the small hexradiate spicules in the interior are not herd but straight, 

 and are, up to the pointed extremity, beset with lateral prongs.^ 



Higgin succeeded in discovering in his Hyalonema cebvjense the true position of the 

 dermal spicules, and Klistermann^ observed in the same year, in Hyalonema sieboldii, 

 the presence of four cruciately disposed anchor-teeth on the extremity of the long tuft 

 spicules. Kiistermann also observed, close to the extremity of a tuft-spicule, that the fine 

 axial canal was crossed by two short transverse canaliculi disposed at right angles to one 

 another. 



An elaborate description of the minute structural relations of Hyalonema sieboldii 

 has been given by MarshalP in his admirable Researches on tlie Hexactinellidse. He 

 calls attention to the peculiar sieve-like perforated plate which covers the upper truncated 

 extremity of the sponge-body. In the large hollow cavity of this species he also 

 succeeded in discovering round embryos of the size of a millet grain or a pea, and 

 exhibiting a central cavity with a small round excurrent opening. The wall consisted for 

 the most part of smooth hexradiate spicules. On the outer surface spindle-shaped 

 spicules occurred ; and long pointed rod-like forms penetrated the wall here and there in 

 a radial direction, and projected for a considerable distance beyond the surface. One of 

 the specimens of the Leyden collection, described by Max Schultze, appeared to 

 Marshall, on account of its diff"erent dimensions, and especially on account of the peculiar 

 condition of the dermal skeleton, which was said to exhibit anastomosing bands of long 

 elastic uniaxial spicules with large cross spicules at the anastomoses, to justify the 

 institution of a new species, which he named Hyalonema affine. Important deviations 

 from the Hyalonema sieboldii type were exhibited by a small (only 7 cm. in length) 

 Hyalonema which Wyville Thomson collected to the north of the Shetland Islands, from 

 a depth of 550 fathoms, and which has been named Hyalonema thomsoni. Instead of 

 the sieve-net, which extends across the upper truncated extremity of Hyalonema 

 sieboldii, a central slender cone, 1 cm. in length, projects freely, and from its expanded 

 base four cruciately disposed narrow ridges extend, forming the ujjper border of four 

 septa which traverse the cavity of the sponge in a radial direction. Another peculiarity 

 of the Hyalonema thomsoni consists, according to Marshall, in the thumb-like prongs 

 which are spirally disposed on many of the tuft-spicules, and which at theii- union 

 with the ridge-like projecting basal portion of the spicule exhibit a canaliculated 

 appearance. 



AVyville Thomson* then briefly noted and figured some particularly striking forms of 

 Hyalonema from the rich collection of the Challenger Expedition. One species, obtained 

 in the vicinity of St. Thomas, from a depth of 390 fathoms, and named by Wyville 



1 Loc. cit., pi. xxi. figs. 4, 5. » Archivf. mikrosk. Anat., Bd. xi. p. 268. 



3 Zeitschr.f. wiss. ZooL, 1875, Suppl.-Bd. xxv. p. 142. * The Atlantic, 1877, vol. i. p. 273. 



