59 



The comparison of sieve-plates of specimens of different ages shows that 

 their growth is accompanied by a growth of the parenchymal principalia in 

 length and thickness and an increase of the width and number of the meshes. 

 The strands forming the sieve-plate-net become broader and then multiply by 

 fission, and new strands are formed, which cut off corners of the old meshes. 



I consider it to be of great importance that the spicules of the gastral and 

 dermal membranes, and the microscleres generally, particularly the graphiocoms 

 and floricoms, have in all the specimens at my disposal the same shape and size, 

 and that they are in the smallest (youngest) specimens only somewhat tender 

 and more slender than in the larger (older) individuals. Everywhere, also in 

 the older specimens, fresh spicules are constantly being formed. These have 

 very slender main- and branch- rays and are remarkable for the slight develop- 

 ment of their stouter parts, as for instance the hand-like terminal discs of the 

 floricoms (pi. X, f. 9. 10). Such slender young spicules are more abundant in 

 young specimens than in older, particularly in perfectly fullgrown ones. 



All the 10 specimens of Euplectella simplex were found near the Andamans, 

 8 (5 small and 3 larger ones) 33km. to the west of middle Andaman Island in a 

 depth of 457 m.=250 fths., and the other 2 (1 small one and 1 half of a large one) 

 between North- and South-Sentinel Island in a depth of 402-439 m. = 220-240 

 fths. 



Euplectella aspera F. E. Sch. 

 Plate XI. 



1895 Euplectella aspera P. E. Seh. in Abh. Preusa. Ak. 1895 pp. 26-29 Taf. III. 



Under the name Euplectella aspera I have described a species of Euplectella 

 from the Indian Ocean, of which only two incomplete specimens were contained 

 in the collection. The smaller specimen, the soft parts of which are fairly well 

 preserved, is 5 cm, long and has a maximum breadth of 2 cm. It represents the 

 low^ half of a straight, slightly inflated, tubular body to the under end of which 

 a short, torn remnant of a root-tuft is attached. 



The parietal apertures measure about 3 mm. in diameter, are rather distant, 

 circular or oval, and arranged, as in Euplectella suherea Wyv. Thomson, not 

 in transverse and longitudinal, but in spiral rows. The similarity to the Atlantic 

 E. suberea is increased by the presence of numerous radial spines, 5 mm. long, 

 projecting freely from the outer surface. These are arranged regularly, and. arise 

 from the crossing-points of the numerous longitudinal and transverse spicule- 

 fibres of the mam skeleton-net. Another point of similarity between the two 

 species is the rough tuberculous, " cork-like " structure of the wall of the tubular 

 sponge, which is 2-3 mm. thick (pi. XI, f. 1, 3). 



