INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 465 



disgorging, lie imagines tlie swallowing them to have been accidental ; 

 and a similar phenomenon carelessly observed may well have given 

 rise to a false interpretation. 



It seems that here we have the true explanation of the occasional pre- 

 sence of nematocysts in the endoderm ; and this explanation Professor 

 T. J. Parker is now inclined to accej)t. As regards the absence of 

 the interstitial cells from the tentacles of Hydra fusca, Mi\ Hartog is 

 not able to confirm him ; on the contrary, they are present, though in 

 isolated patches, and not forming a continuous network as over the 

 body. The best way to demonstrate these is, having killed a Hydra 

 extended on a slide by letting fall a drop of 1 per cent, osmic acid on 

 it, to at once wash away the acid by a flood of absolute alcohol, and 

 then after a few minutes to stain with ammoniacal carmine or picro- 

 carmine. If the Hydra is now examined in glycerine under a power 

 sufficiently high to focus successive layers, the presence of interstitial 

 cells can be made out. Owing to their dispersion, the want of them 

 in a section becomes very slight evidence for their absence. 



Porifera. 



Octoradiate Sponge — Development of Sponge-Buds.* — The 



sponges here treated of by Professor Sclenka are interesting, as coming 

 from a locality — Rio Janeiro — where the sponge-fauna has been little 

 studied hitherto. Two genera, the one belonging to the Ancorinid, 

 the other to the Corticate group of siliceous sponges, are mentioned. 

 Of the one, Tetilla 0. Schmidt, which the author re-characterizes, he 

 states that it is monozoic and dicecious ; both males and females mul- 

 tiply by discontinuous gemmation. One new species, T. radiata, was 

 found in mud ; it is of a blush-red colour. The single osculum leads 

 into a funnel-shaped cavity, from which radiate four short, wide canals, 

 which each divide into two, and ultimately end in the ciliated cham- 

 bers. T. eiq^locamos 0. Schmidt was also found, and displays the 

 same essential arrangements of the canals, but with less regularity. 

 An octoradiate arrangement is the result of the bifurcation of the four 

 primary radial canals. This, however, is not to be regarded as indi- 

 cating a transition to the Cculenterata, for it is brought about by the 

 development in this jiarticular case of a root-tuft, and is not mani- 

 fested in the arrangement of the pcrijiheral ciliated chambers. How- 

 ever, it serves to show how radial symmetry may arise out of asym- 

 metry, and perhaps to mark an outlying section of the Sjiongida distin- 

 guished by a somewhat fixed radial arrangement. It is worthy of notice 

 that the quadriradiato spicules which project from the body serve not 

 only to anchor it, but also to capture minute prey. 



Gemmae are produced in great niunbers — forty to one hundred on an 

 average — ^in almf)st all individuals. The commencement of the bud is 

 caused by multiplication of mesoderm cells just under the dermis 

 round one or a few spicules, until a globular mass full of cells, and 

 containing twelve to twenty ciliated chambers, is produced ; this pro- 

 trudes from the surface of the sponge, and is eventually projected from 

 it on a bundle of spicules. Meanwhile, double-pointed lin«.;ar spicules 



* 'Zcitsclir. wiss. '/,'vA.' xxxiii. (1S7'.>) p. 1(!7 ('i platts). 



