46 Mr. T. Higgiu on the Structure of the 



viti-eoiis coating being of the same nature as the spicules them- 

 selves, their outlines become lost to sight in it ; it is impossible 

 to distinguish them and trace their form and shape. Most, if 

 not all, of the specimens which are brought to this country from 

 the Philippine Islands are of this rigid character ; and conse- 

 quently the structure of the network remains undescribed. In 

 your specimen, however, we have part of the network vitrified 

 and part of it unvitrified ; and in the unvitrified portion all 

 the spicules are easily traceable and distinguishable, lying in 

 the position they are destined to occupy in the rigid skeleton, 

 ready for the silicious coating to be poured over them. 



This, I understand, is the sponge to which Prof. Wyville 

 Thomson alludes in his letter from the ' Challenger,' Avhich 

 appeared in the number of ' Good Words ' for July last, where 

 he speaks of the examples of Euplectella which were brought 

 up in the trawl off Cape St. Vincent, the spicules of Avhich 

 were not soldered together, but were in the same condition 

 throughout as those of a specimen of Euplectella in the Liver- 

 pool Museum. I learn, too, from Mr. H. J. Carter, of Bud- 

 leigh-Salterton, that " Dr. Semper, of Wiirtzburg, had seen 

 specimens of Euplectella aspergilliim without any vitrified 

 fibre, which he had viewed as young specimens in which 

 the wliole would have become vitrified if they had remained 

 long enough in their natural place of growth — that, in fact, 

 the flexible or unvitrified is the primary state of this species." 

 The groundwork of the square meshes is an arrangement of 

 very large four-rayed spicules, the arms of which lie longitu- 

 dinally and transversely ; and so large are these spicules that 

 they do not require to be measured under the microscope by 

 the 100th or 1000th of an inch, but may be measured with 

 an ordinary pocket-rule ; each transverse arm extends over 

 three to four of the square areas, so that from the tip of the one 

 to the right to the tip of the one to the left is three quarters of 

 an inch to an inch, and the longitudinal arms are still longer. 

 I may here remark that these are genuine four-rayed spicules, 

 and that at the central spot there is no appearance of suppressed 

 arms. As the square areas only measure about one eighth 

 of an inch each, it will be evident that the long arms of these 

 spicules must extend towards eacli other, meet, and lie along- 

 side one another, the tapering end of one extending up to- 

 wards the thickest part of another. Along these interlocking 

 arms are placed long, straight, and very slender spicules, which 

 are spined from the exti-emities for a considerable distance along 

 the shaft (PL III. fig. 7). 



The diagonal lines and all the fine filaments are the long- 

 arms of four-rayed and six-rayed spicules, only three of 



