246 ANATOMY AND PHYSIOLOGY 



Jio. 



the peltate apex of the spiculum ia irregularly circular, 

 and etltirely devoid of the complex and beautiful 

 sinuous foliations that render the adult spicula such 

 elegant objects. Kg; 102. X 260 linear. As the 

 development proceeds it assumes a trilobular shape. 

 Kg. 103, X 160 linear, and the margins are slightly- 

 indented or serrated. 



In a further advanced condition, the sinuation of 

 the margin becomes deeper and more complex, as 

 represented in Figs. 104, X 160 linear, and 105, 

 X 160 linear, until at last it becomes, in the fully 

 developed peltate apex, so deeply and irregularly 

 sinuated as to nearly obliterate all traces of its ori- 

 ^nal trilobular character (Kg. 106). X 130 linear. 

 Kg. 107, X 160 linear, represents a side view of a 

 Spiculum exhibiting the form and comparative length 

 of the shaft. Fig. 108, X 260 linear, exhibits the 

 furcated terminations to tvi^o out of the three radiating 

 canals of the apex of the spiculum. 



RETENTIVE SPICULA. 



109. Simple bihamate. — ^Acerate spicula, having each end 



of the spiculum curved in the form of a hook in 

 the same plane and towards each other. From 

 Halichondria variantia, Bowerbank, X 1060 

 linear, Page 43. 



110. Reversed bihamate spicula. — Having each end of 



the spiculum curved in the form of a hook in the 

 same plane, but in opposite directions to each 

 other. From Halichondria incmstans, Johnston. 

 X 1060 linear. 



111. Contort bihamate spicula. — Having each end of 



the spiculum curved in the form of a hook but in 

 planes at right angles to each other. From Hali^ 

 choiidria incmstans, Johnston. X 1060 Unear. 



