r.Y E. F. HALT.MANN. 



465 



Their curvature, in proportion to tlieir 

 lengtli, is sliglit, and often affects only a 

 very limited portion of the central region 

 of the spicule, the actines throughout 

 nearly their whole length remaining 

 straight: they are frequently, theiefore, 

 more correctly to be described as sym- 

 metrically bent, than as curved. Except 

 in this respect, and in their much greater 

 length, they most resemble, on the whole, 

 the megascleres of T. diyitatm^ var. xtroii- 

 Liyhifus ; the strongyla, however, differ 

 from those of the latter, as^well as from 

 those of the other two species in which 

 they occur plentifully, in that they are 

 ne\er quite cylindrical, but always taper 

 slightly, with nearly uniform gradualness, 

 from the middle to either end. Their 

 diameter is rarely more than one-fiftieth 

 of their length, which ranges from about 

 330 to 560 /x. 



Microschres. — The spiruUv are, without 

 exception, of less than 2 complete turns, 

 and a very considerable proportion 

 (amounting to at least 25%) are of less 

 than 1 turn — i.e., are more or less Q- 

 shaped; they frequently attain to 2 "5 or 

 3 /J. in stoutness. Rod-shaped derivatives 

 are common, but are very seldom more 

 than 8 /i in length. 



The mici'ostrongyla — which in most 

 parts of the sponge are fairly abundant — 

 are, with rare exception, centrotylote and 



Text-fig. 2. 

 rather slender, very seldom exceeding Trachycladns fu.itit/Kfns. 



'I-Oixin diameter; but occasional stouter Megascleres : a, tiom 

 " the stalk; /', tioni tlie 



ones without the dilatation also occur, bianches. 



38 



