ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 75 



endodermal layers have a digestive function ; and that in the sponges 

 the germinal layers are indifferent. 



Note on Sponges.* — Two species of Leucandra {L. cramhessa 

 and L. aspera), supposed by Hackel to be distinct, are shown by 

 G. C. J. Yosmaer to be merely varieties of the same form, since their 

 anatomy does not show sufficiently constant differences, and there is 

 every transition between the two ; the polymorphosis of L. aspera 

 is very remarkable, but may be accounted for by different conditions 

 of life ; these, however, require working out. 



Hackel found in some calcareous sponges the cloacal cavity 

 divided by irregular membranes ; in L. aspera these were frequently 

 found by Vosmaer ; the canals and lacunae formed by the anastomosis 

 of these septa are quite different of course from the large excurrent 

 canals, since they are remains of the primitive cloacal cavity, while 

 the latter are developed as outgrowths from it. 



The relationship between the Eenieridee and the Ceraosponges is 

 undoubtedly a very close one, and v. Lendenfeld has stated that these 

 Monactinellids probably have arisen directly from the Ceraospongias. 

 It may, however, be the case that the Ceraospongiae have originated 

 from the Monactinellids, and the following facts seem to favour this 

 supposition. In the oldest sponges, the Hexactinellids, there is no 

 trace of spongin in recent or in fossil forms, and therefore it may be 

 assumed that the cells which produce spicules are of an older form 

 than those which produce spongin, and it follows that the Ceraospongiae 

 are younger than the Monactinellids, though this is not known on 

 palseontological grounds. In the second place, the canal system of the 

 Monactinellids is less complicated than that of the Ceraosj^ongiae. It 

 appears, however, that there is spongin in Beniera, and that therefore 

 some mesoderm cells of siliceous sponges gradually change into real 

 spongoblasts, and that thus through certain qualities of the sea water 

 or other causes true horn sponges have been formed. 



Modification in the form of Sponge Spicules.f — E. Potts describes 

 a singular modification in the spicules of Meyenia Leiclyi found 

 incrusting old pipes from water-works at Philadelphia, some portions 

 of which were so deeply coloured with rust that the statoblasts seemed 

 to be mere pseudomorphs in iron oxide. Fragments were boiled in 

 nitric acid and compared with similarly treated portions which were 

 free from discoloration. 



The mature normal skeleton spicule of the latter is smooth, 

 robust, shorter than that of any other American species, and the 

 fine line of the axial channel very rarely visible ; but in the former, 

 whilst the size and exterior appearance of the spicul^e remain the 

 same, the axial channel has become a wide canal, open at both ends, 

 and occupying more than one-half the breadth of the spicule. The 

 birotulate spicules, usually short and of a peculiarly substantial 

 appearance, with entire reflexed margins, can with difficulty be detected 

 as mere ghosts of their normal shapes. The two disks rarely remain 



* MT. Zool. Stat. Neapel, v. (1884) pp. 483-93 (2 pis.), 

 t Proc. Acad. Nat. Sci. Philad., 1884, pp. 184-5 (1 pi.). 



