266 ANATOMY AND PHYSIOLOGY 



Fig. 



and the rotulse are cleft almost to the point of union 

 with the shaft. The number of the curved spines 

 vary ; in one rotula there were as many as ten, but 

 the usual number is five or six. An average- 

 sized specimen measured t^th of an inch long; 

 diameter of the rotulse, ^^th of an inch ; and dia- 

 meter of the shaft, ^m^h. of an inch. 

 221. Ineqxti-birotulate. X 660 linear. — Thisspiculum 

 223. exhibits a gradual transition from the fully de- 

 veloped birotulate to the completely boletiform 

 tribe of spicula. It occurs in Spon^illa paidula, 

 Bowerbank, from the River Amazon. It is a stout 

 fully developed form, and the whole of them ex- 

 hibited, as nearly as possible, the same proportions. 

 Prom both terminations of the shaft a number of 

 minute radial canals, represented in Fig. 222, pass 

 from the centre to the circumference of the rotulae, 

 and in one of the large ones I counted twenty 

 radial canals. The rotulse are flat, or very slightly 

 convex outward near the centre, and the margins 

 are perfectly entire. Pages 60, 61, and 137. 



223. Boletiform. X 660 linear. — The form of this 

 spiculum is very like that of the common edible 

 mushroom when fidly grown. The large discal 

 end is convex externally, and has the margin entire. 

 The shaft is nearly of the same diameter through- 

 out its length, and occasionally it has one or two 

 large spines projected from it, near the middle and 

 at right angles to its axis. 



The small end is more or less lentiform, but it is 

 frequently very irregular both in size and shape. 

 Prom the ovary of Spongilla reticulata, Bowerbank, 

 River Amazon. Pages &0, 187. 



/ 224. Boletiform: slender, x 660 linear. — 'This grace- 



[225. fvd and elegant form of spiculum occurs at the inner 



surface of the crust of the ovary of Spongilla re- 



curvata, Bowerbank, from the River Amazon. The 



