BY E. P. KALLMANN. 



289 



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to maceration, but after prolonged ti'eatment, aided 

 by washings with a pipette, it becomes reduced to a 

 reticulation of fibres composed of a substance nnu;li 

 resembling spongin, entangled with which, and ap- 

 parently for the most part independent of it, are 

 numerous indifierently oriented oxea. Many of the 

 apparently free spicules, however, prove, on close sci'u- 

 tiny, to be ensheathed, over portion at least of tlieir 

 length, with a thin layer of spongin continuous with 

 that of the fibres; and the long spicules (subtylo- 

 strongyles) which project from the core, are likewise 

 found to be held in position by a partial covering of 

 spongin. The sponginous fibres are not provided with 

 an axial core of longitudinally disposed spicules. 



Skeleton. — The skeleton of the axial region consists, 

 in addition to the spongin-reticulation and the irregu- 

 larly disposed oxea, of ill-defined longitudinal strands 

 of loosely associated oxea and subtylostrongyla. The 

 reticulation of spongin-fibres is exceedingly irregular 

 in pattern, and the fibres themselves are very vari- 

 able in stoutness and uneven in their outlines. The 

 spongin has a faintly brownish-yellow tint, and is of 

 low^ refractive index, and is readily stainable. 



Fig. 1. — SolUisella diqitata. a, Subtylostrongyla. a', Basal ex- 

 tremities of ditto, h, Oxea. h\ Extremities of oxea. 



Immediately surrounding the core-region, and forming the 

 inner limit of the subcortical layer, is a narrow belt of longi- 



