Variety o/*Meyenia fluviatilis. 455 



Obs. Described in the dry state. The Calumet specimen 

 is remarkable for presenting the birotulate spicules in all 

 stages of development loose in the tissue of the sponge, where 

 it may be seen that the shaft is the first part to be formed, 

 commencing in two minute elongated portions, constricted 

 yet connected by a delicate thread in the centre, and thus 

 strongly foreshadowing the characteristic hourglass form of the 

 fully-developed spicule ; while, on the otherh and, the " Ditch- 

 ley's " specimen presents the whole statoblast in all stages 

 of development, from a minute and shrunken, shapeless 

 dried bit of yellowish sarcode, to the fully developed form 

 of this reproductive body. When first recognizable, in its 

 present dried state, as a reproductive organ, it presents an 

 ovoid or globular form of a yellow colour, about half the size 

 of the matured object, composed of a toughish yellow trans- 

 parent capsule, filled with globules or cells of a refractive 

 matter, which can be plainly seen through this envelope ; 

 globules or cells varying in diameter under 5-6000ths in., 

 consisting of a semifluid refractive substance, which, although 

 evidently undergoing subdivision in the larger portions, is 

 sufficiently consistent to retain its globularity when forced out 

 into the water by rupture of the capsule ; so arranged as to 

 fill up the latter except at one point in the end, which 

 presents a minute, circular, transparent area, the future hilous 

 opening of the chitinous coat ("?). After this the capsule be- 

 comes transformed into the shape of the fully-developed 

 statoblast, but still retaining its yellow colour, and now 

 covered by the layer of birotules alone, with their inner 

 rotules resting on the capsule, now also seen to be the 

 chitinous coat ; to which is then added the white microcell- 

 structure which fills up the space between the birotules, and 

 thus completes the formation of this reproductive body. 



The only variety of Meyenia fluviatilis that can be con- 

 founded with it is that of Bombay, on account of the greater 

 length of the birotules, which bear the proportion of six in the 

 former to seven in the latter ; but here the shaft is equal in 

 thickness throughout and the rotules denticulated to the umbo 

 or centre, rather than fringed or striated towards the circum- 

 ference only, much as represented in my original description 

 of 1849 ('Annals,' vol. iv. pi. iii. fig. 6, d) ; not like that 

 given by Dr. Bowerbank in 1863 (Proc. Zool. Soc. pi. xxxviii. 

 fig. 4), which must have been taken from an accidental form, 

 and therefore is misleading. On the other hand, the skeletal 

 spicule in the Bombay variety may be spiniferous as well as 

 smooth ; while I have never seen any spiniferous ones in the 

 Calumet variety. 



