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



of the skin skeleton are said to be completely closed by a thin transparent membrane, 

 and in the latter, groups of small " quadrifurcate hexradiate spicules" occasionally occur. 

 In the interior of the soft body Bowerbank thought he could perceive numerous 

 " gemmulfe" surrounded by a simple membrane. 



In Marshall's research on the Hexactinellida, published in 1875,Mhere is a detailed 

 account of the Euplectella oireni, Marshall and Herklots, from Japan, which had been 

 already shortly described by Marshall and Herklots. This species is accurately com- 

 pared with the Philippine EuplecteUa aspergillum, which Marshall had also the oppor- 

 tunity of studying in a young specimen, with as yet entirely unfused spicules. 



While there is a great general resemblance in the forms and position of the spicules, 

 as is particularly obvious in comparing EuplecteUa oweni with EuplecteUa aspergillum, 

 there never occurs that fusion of the main spicular bands which occurs in Evp>lectella 

 aspergillum when it becomes old, and which leads to the formation of the elegant 

 lattice-like framework. While, moreover, Euplectella aspergillum, which is always 

 much bent, presents an approximately round tube, continually increasing in diameter 

 from the base to the free extremity, and is provided laterally with ridge-like, oblique, 

 outwardly directed elevations, and at the extremity with a cuff, bounding the terminal 

 sieve-plate, Euplectella oweni consists of a perfectly straight tube which is oval in 

 transverse section, and without external ridges or a terminal circular cuif. From the 

 broadest part of the tube, which is situated about the boundary between the inferior and 

 middle third, the diameter diminishes very gradually upwards. The closure is efi'ected 

 by a sieve-plate which is somewhat strongly arched outwards. 



Sir C. Wyville Thomson^ pubhshed in 1877, a short description of a new species of 

 Euplectella {Euplectella suberea, Wyville Thomson), of which three more or less injured 

 specimens, figured in a woodcut {loc. cit. p. 29), were collected to the west of Gibraltar. 

 It may be well here to repeat the words of the highly respected leader of the expedi- 

 tion : — " The fine species for which I propose the name Euplectella suherea, of which three 

 specimens, all unfortunately more or less injured, were taken in the trawl, forms a hollow 

 cylinder about 25 cm. in length by 5 cm. in diameter. The walls are composed, as in 

 Euplectella aspergillum, of a fundamental, square meshed, siliceous network, bands of 

 spicules running longitudinally from end to end of the sponge, and transverse bands 

 intersecting these at right angles. The spicules are in some cases straight and smooth, 

 frequently four projecting knobs ranged round the centre of the shaft of the spicule 

 show that, in essential form, the spicule is six-rayed, and often one of the side rays is 

 strongly developed and projects to a distance of half an inch or more from the surface 

 of the sponge. The spicules are all free from one another, and those composing the 

 bands can easily be teased asunder w\i\\ a pair of needles. In this species, as in 

 Eupjlectella aspergillum,, the corners of the square meshes are filled up, a pale brown 



1 Zeitschr.f. wiss. Zool, Bd. sxv. Suppl., p. 142. 2 xiie Atlantic, vol. i. pp. 138-140. 



