REPORT ON THE HEXACTINELLIDA. 59 



specimens of Euplectella aspergillum, particularly one in the Museum of Liverpool, are 

 in this condition, and I am not yet prepared to say whether all may not be thus soft at a 

 particular stage of growth." 



Higgin found that a rigid, firmly united, siliceous framework was only present on the 

 under portion of the sponge, while the upper part appeared C[uite pliable. In the inferior 

 portion the skeletal spicules were provided with a siliceous sheath, and were firmly 

 connected by means of this ; above, on the other hand, this union of the spicules was 

 entirely absent. 



According to Higgin, large four-rayed spicules form a fundamental quadrate network. 

 The arms of these spicules lie in exactly longitudinal and transverse directions, and are 

 apposed to one another. The arms of the cross spicules, which are about 2 cm. long, 

 stretch across three or four meshes, and the longitudinally directed arms are still longer. 

 Close to the four-rayed spicules (and united with their arms in a bundle-like manner), 

 are simple, long, rod-like needles with thorny ends. The long arms of the three-rayed, 

 and less frequently also of the four- or six -rayed spicules, are employed in the formation 

 of the oblique fibrous bands. In these spicules two approximately equal arms extend in 

 one straight direction, while the third, or the remaining two or four arise transversely, 

 either straight and at right angles, or slightly bent. The spindle-like swollen extremities 

 of the arms are thickly covered with fine spines. In the description of the simple spicules 

 Higgin does not add anything to the researches of Clans and Carter, but corroborates the 

 opinion already expressed by Semper, that the entire skeleton of Euplectella aspergillum 

 always consists in the young state of isolated spicules, which, only at a later stage, 

 become partially fused, and more or less firmly united by the deposition of layers of 

 siliceous substance. This process of fusion begins in the inferior portion of the lattice- 

 like tube. 



A communication by Bowerbank ^ gives a more minute account of the arrangement of 

 the loose spicules in the tissue of Euplectella aspergillum. There is here to be noted an 

 important advance in our knowledge of the dermal skeleton. Bowerbank first recognised 

 that, for the support of the dermal layer, the whole surface is provided with a system of 

 radially directed, floret-like, six-rayed spicules, and that each of the centrally directed 

 longest rays of these is apposed to a more deeply seated six-rayed spicule, while the four 

 lateral rays are applied to the corresponding lateral rays of the four adjoining spicules of 

 similar formation, and thus form a regular network of approximately equal quadrate 

 meshes, while the distal ray, which is of about the same length as the lateral rays, 

 projects radially outwards. Each of these freely projecting, radial, distal rays, bears 

 terminally one of these elegant structures which are designated by Bowerbank "floricomo- 

 hexradiate spicules." These ap23ear in no other region of the soft body of this sponge, 

 and are regarded as protective weapons against small worms, &c. The quadrate meshes 



1 Ptoc. Zool. Soc. Land., p. 503, 1875. 



