Plate 52 



Fig. 1. Phyllospongia aliena. From a vertical section, showing a radial 

 fiber, r. f., containing sand grains and foreign spicules, with con- 

 nectives crossing it. One connective, a, starts from the radial fiber ; 

 others are all cemented to it by spongin; sy, a synapticulum. X150. 



2. Hircinia mutants. Two main fibers, m. f., and connectives, latter rang- 



ing from simple fibers to fenestrated plates. Connectives not in- 

 dicated along free edge of right fiber. X 45. 



3. Phyllospongia aliena. Two connectives crossing one another cemented 



together by spongin, sp. X300. 



4. Hircinia mutans. A main fiber, m. f., with connectives meeting it on 



one side. Origin of connectives on other side of fiber not shown. 

 X45. 



5. Phyllospongia aliena. Connectives. One connective, a, ends in a 



spongin expansion on the side of another ; in the expanded portion 

 strata, parallel to the surface, are faintly distinguishable. The free 

 end of another fiber, b, appears; its outer border is here no more 

 cuticular in appearance than is the case with spongin which cements 

 fibers together ; terminal region faintly stratified. An axial medul- 

 lary streak is distinguishable in both fibers, a and &, near the end. 

 X300. 



6. Hircinia mutans. Two main fibers, m. f., with connectives. One of the 



connectives is a fenestrated membrane of considerable width ; the 

 other is narrower. The roots (fenestrated expansions) of con- 

 nectives have spread out extensively along the sides of the primi- 

 tive (simple, solid) main fibers. Origin of connectives from far 

 side of right fiber not shown. X45. 



7. Hircinia, mutans. Two main fibers, m. f., with connectives. Latter in 



part simple, meeting the main fibers in the usual way, in part 

 (above) combined to form a fenestrated membrane. Connectives 

 not indicated along free edge of right fiber. X45. 

 522 



