5-1 THE VOYAGE OF H.M.S. CHALLENGER. 



a transverse, slightly convex sieve-plate closes that end which he regarded as the inferior, 

 while Alcyoncclhun speciosum appeared to exhibit a sim^ile inferior extremity. Further, 

 as he had inadvertently read the word Alcyoncellum, Alcyonellum, he maintained that, 

 even if there was a generic agreement between his Sponge and that described by the 

 French investigators, yet the name Alcyonellum must be changed since it had been 

 already bestowed by Lamarck on a Bryozoon. Owen also erred in regarding Alcyonellum 

 gelatinosum, Blainville, as synonymous with Alcyoncellum speciosum, Quoy and Gaimard. 

 In a paper which appeared in 1857,' Owen described a second species of the same 

 genus under the title Euplectella cucumer. This he distinguished from Euplectella 

 aspergillum by its barrel-like form, by the absence of the oblique ridge and of the cuff- 

 like collar at the extremity, which in this species is truncated and closed by a sieve- 

 plate. The single specimen u23on which the description was based was presented to 

 Captain Etheridge by the King of the Seychelles. 



The generic characters of Euplectella, which were more definitely formulated in this 

 than in the previous memoir, are as follows : — "A cjdindroid hollow form of body, closed 

 at the wider end Ijy an irregular network, and at tlie narrow end by the terminal tuft of 

 finer filaments into which the parietal fibres are there resolved. The parietal fibres, or 

 those that constitute the wall of the cylinder, are regularly disposed, and intersect each 

 other at definite and nearly equal distances throughout its extent. They consist of 

 longitudinal, transverse, and oblique fibres, the latter being of two kinds, winding spirally 

 round the cylinder, but in ojDposite directions. The longitudinal and transverse fibres 

 are the thickest ; they are arranged at intervals of from one to two lines, averaging one 

 line and a half apart, and divide the cylinder wall into square spaces of about the latter 

 diameter. The longitudinal fibres are external to the transverse ones, to which they are 

 bound by the oblique or spiral fibres ; these are, some external, some internal, to the 

 others, and they close by their decussation alternate quadrate intervals between the 

 longitudinal and transverse fibres. The angles of the alternate open squares are 

 intersected by finer and less regular oblique fibres, which reduce their area more or less 

 to a circular form." 



The fact that, in the specimens on which the description of EuplecteUa cucumer was 

 based, the tuft of long siliceous spicules included a number of foreign bodies, led Owen to 

 believe that the fixing of this sponge, and also of Euplectella asiyergillum, was not 

 efiected by means of a sieve-plate, but by the long hair-like tuft ; and accordingly, that 

 the natural position was the inverse of what he had formerly described in regard to 

 Euplectella aspergillum,. 



A treatise by Bowerbank, which appeared in 1858,^ contained a detailed descri^ation 

 of sponge spicules. In this memoir several of the beautiful microscopical spicules which 



1 Trans. Linn. Soc. Land., vol. xxii. (2), pp. 117-124, pi. xxi. 



2 On the Anatomy find Physiology of the SjjongiaJa;, Pliil. Trans., vol. cxlviii. p. 279, pis. xxii.-xxvi. 



