HOLASCUS EDWARDSII. 25 



thickening arise backwardly directed teeth usually six to eight in number. The 

 anchor-teeth of the same anchor being more or less unequal in size, shape, and 

 position, the anchors themselves appear more (Plate 20, figs. 5, 6, 16, 18) or less 

 (Plate 20, figs. 7, 8, 19, 20) irregular. The anchor, that is the terminal style to- 

 gether with its teeth, is 45-72 ix long and 32-50 ^ broad. 



The axial thread of these spicules extends quite to the end of the terminal 

 anchor-tyle. Within this tyle it is thickened in a spindle-shaped manner and 

 here measures 2.5-4 /^ in maximum transverse diameter (Plate 20, figs. 5-10). 

 This terminal thickened part of the axial thread is granular, and irregular in 

 outline. From it arise a number of branchlets, up to 1 m long, usually very 

 oblique, strongly inclined towards the end of the anchor. According to F. E. 

 Schulze's figures ^ in other species of Holascus the axial thread of the anchoring 

 spicules in the terminal anchor-tyle is not thicker than elsewhere. In describ- 

 ing H. tenuis this author, however, says^ "Der Achsenkanal durchsetzt den 

 Kolben" (that is, the terminal anchor-tyle) "bis dicht an seine untere Spitze 

 und erfahrt hier zuweilen eine kleine terininale Verbi'eiterung oder Zerteilung 

 in ein schmales Buschel mehrerer Endauslaufer." 



The thickening of the distal end of the spicule and of its axial thread 

 in the anchor-spicules of Holascus edwardsii is doubtlessly correlated to the 

 shortening of tlie distal ray. I think that the influence which prevented the 

 distal ray from obtaining a length commensurate with the length of the proximal 

 ray, also caused the thickening of the ends of the distal ray and its axial thread, 

 and the formation of the oblique branchlets of the terminal swelling of the latter. 

 This influence may be inherent, arising naturally at a certain period of develop- 

 ment in the spicule-building cells themselves, or it may be due to the resistance 

 which the distal ray encounters at its tip whilst it is being pushed outward 

 (downward) in consequence of the continued longitudinal growth of the proximal 

 ray. The latter alternative seems a priori the more probable, but I am rather 

 inclined to favour the former since young anchoring spicules, the distal ends 

 of which do not protrude over the surface and have not yet reached the deep-sea 

 deposit (ooze) into which they are afterwards driven, already possess a distal 

 anchor-tyle. 



The terminal thickening of the axial thread with its branchlets in the 

 anchor-tyle is in many respects similar to certain structures found in the cladomes 



1 F. E. Schulze. Rept. Voy. Challenger, 1887, 21, pi. 16, figs. 11, 13 H.fibulalus; Hexactinelliden des 

 Indischen Oceanes. II. Abh. Akad. Berlin, 1895, 1896, taf. 1, fig. 6 H. robustus; Ergeb. Deutsch. tiefsee- 

 exped., 1904, 4, taf. 1, figs. 4, 6 H. tenuis. 



2 F. E. Schulze. Ergeb. Deutsch. tiefsee-exped., 1904, 4, p. 6. 



