GEODIA AGASSIZII. 115 



Also in the immature specimen from Station 4228 spicules protruding up to 5 

 mm. beyond the surface occur. From these observations I infer that large 

 spicules are protruded and a spicule-fur is thus formed by all these sponges, 

 and that this has been wholly or partly lost during life or after capture. 



Larger apertures (oscules) are absent, but minute holes in the sterraster- 

 armour are observed in large numbers. Minute holes of two different sizes can 

 be distinguished. The larger, which are clearly visible to the unaided eye, 

 and through which the efferent cortical canals pass, are restricted to certain areas 

 of the surface. The smaller, which are not visible to the naked eye and through 

 which the afferent cortical canals pass, occupy the remainder of the surface. 

 In one of the specimens from Station 4199 the area perforated by the large 

 efferent holes is roughly circular in outline, 18 mm. in diameter, and slightly 

 concave, thus forming a shallow depression. In the other specimens the effer- 

 ent areas are not depressed. In the large specimen from Station 4139 there are 

 two efferent areas, one a horseshoe-shaped zone 20 mm. broad and 64 mm. 

 in total diameter, the other an irregularly circular patch 15 mm. wide. In 

 the smaller specimens there are one or two, rarely three, generally more or less 

 circular efferent areas 8-24 mm. in diameter. The holes piercing the sterraster- 

 armour in these efferent areas (Plate 26, fig. 13) are circular and measure 300- 

 700 n in diameter, their centres being 1-1.5 mm. apart. 



Concerning the mode of attachment it is to be noted that the young specimen 

 from Station 4228 has grown quite over part of the hexactinellid skeleton-net 

 which forms its support, the siliceous bars of the latter partly penetrating the 

 sterraster-armour of the Geodia and entering its choanosome which surrounds 

 them as if they formed a portion of the true internal skeleton of the Geodia. 



Most of the specimens are light brown in colour. The larger one of the two 

 from Station 4193 has a few extensive darker, rust-brown patches on the surface. 

 Of the eight specimens from Station 2886 some also are light brown, while 

 the others are dark blue. The specimens from Stations 4228 and 4551 are 

 lighter in colour than the others, nearly white. The true colour of these sponges, 

 when preserved in spirit, is probably light brown or white; the rust-brown and 

 dark blue pigmentations of some of the specimens may possibly have been pro- 

 duced after capture. 



The sponge has a cortex, which is in the adult specimens about 1 mm. thick 

 and composed of three layers, the dermal layer outside, the sterraster-armour 

 layer in the middle, and a fibrous layer within. The dermal layer is in the young 

 specimen from Station 4228 (Plate 32, figs. 8, 11, 12) and in several of the adult 



