244 ANATOMY AND PHTSIOLOGT 



Fig. 



94. DoLioLATE CYLINDRICAL. X 175 linear. — From a 



sponge nearly related to Ecionemia, Bowerbank. 

 Locality unknown. Prom the similarity of the 

 form to Pig. 93, it is probably a tension spi- 

 culum. 



95. Inflato-cylindrical. X 660 linear. — This form of 



spiculum is very minute. It is slightly curved, 

 and has a single, well-defined bulbous inflation near 

 the middle of the shaft, but in this respect, as well 

 as in size, there is, comparatively, a considerable 

 amount of variation. The normal condition of the 

 inflation is equidistant from the ends of the spi- 

 culum, but in some cases it is not more than a 

 third of the length of the spiculum from one 

 end of it. The only sponge in which I have found 

 this form is Hymeniacidon ficus, Bowerbank, where 

 it occurs in the dermal membrane in great pro- 

 fusion. 

 Tricurvato-aceratb. X 260 linear. — This form of 

 spiculum has always three curves in the course of 

 its length, one at the middle of the shaft, and one 

 near each termination, the terminal ones curving in 

 the same direction, and always opposite to that of 

 the central curve. 



These spicula vary greatly in form and proportions 

 in difierent sponges, and frequently even in the same 

 species. The normal form is that of three curves of 

 about equal value, (Pig. 96,) but sometimes, as in 

 Pig. 97, the central curve is very much the larger of 

 the three, while in Pig. 98 we find the extreme con- 

 dition of the form, the spiculum being comparatively 

 straight, with a very small curve in the centre of the 

 shaft, and the terminations exhibiting only the rudi- 

 ments of curves in an opposite direction to the middle 

 one. They are usually very much more slender than 

 the spicula of the skeleton, and are comparatively of 

 rare occurrence in every species in which I have found 

 them. I have never seen them in situ with the ter- 



