120 



THE SPONGES OF THE WEST-CENTRAL PACIFIC 



Or 



Text Figure No. 74. Spicules of Myrmekioderma tylota. A : Acanthoxea of the abundant 

 type, X 182. B: Oxea with only the ends slightly spined, X 182. C: Smooth strongyle, 

 chiefly ectosomal, X 182. D: One end of a spicule such as A, but X 781. E: One end 

 of a spicule such as B, but X 781. F: One end of a spicule such as C, but X 781. 



G: Tylote microsclere, X 781. 



1 to 3 mm wide. These pore cracks separate the surface into rounded or 

 polygonal islands. Inasmuch as oscules are conspicuously lacking, it further- 

 more must be true that some of the openings in these cracks shall be exhalant 

 and others are inhalant. 



The ectosome is quite complicated. On the very outside, there is a 

 region marked by spicules protruding here and there, so that the term hispid 

 almost is warranted. Among these spicules are numerous bits of foreign 

 material. This layer is about 150 jx thick, and some of the spicules protrude 

 an additional 100 /x past the detritus. Below this there is a layer of flesh ar- 

 ranged in horizontal strands, making a dermis 30 ^ thick. Below this second 

 layer are extensive subdermal spaces about 220 /x high. The ceiling of this 

 subdermal space is held up by numerous columns of spicules about 40 ju. to 

 50 /x in diameter. In this subdermal space, particularly in Specimen No. M. 

 420, there occur numerous embryos about 75 \x to 175 /x in diameter. These 

 take various stains very deeply. Below, the endosome is marked by an im- 

 mense number of spicules packed together in confusion, pointing in all di- 

 rections. The flagellate chambers are oval and upwards of 60 fx in diameter. 



