INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 971 



centimetre in diameter ; the body is regularly globular in form, 

 and is often found attached to the internal surface of some shell 

 (^Terebratula). It is of a clear yellow colour, sometimes darkened 

 to brown ; the regularity of the external form is seldom so well 

 marked as in the large and small specimen figured in Fig. 5, and, as 

 a rule (see Figs. 1-4), there are conical or filamentous projections 

 from its surface. The strange ajipearance produced by these projec- 

 tions leads one at first to sujipose that they are parasites ; this view 

 is shown to be incoi-rect by a closer examination. The most frequent 

 arrangement is shown in Fig. 1, where we find ovoid or pyriform buds, 

 romided at one extremity and at the other passing into a more or less 

 delicate stalk, ()f varying length. Sometimes (Fig. 1 a, 2 a) the buds 

 are globular, and these are seen to be " covered with that layer of 

 organic matters which is characteristic of an adult sponge " ; these 

 buds may even surpass in diameter the smaller specimen shown in 

 Fig. 5. The foot or process which supports the bud is merely a deli- 

 cate cylindrical filament, the length of which may be as great or greater 

 than the diameter of the parent sponge (Fig. 3). In Fig. 8 we have 

 an example of the dichotomous division of this filament. In some 

 cases (see Fig. 7) we may find examples of buds of the second order, 

 or (as in Fig. 6) a number of secondary buds (b, c) may arise from 

 the primary one (a), and these may be in various stages. A tertiary 

 bud (d) may also be seen arising from the stalk of a secondary 

 bud (c). 



The following is an account of the development of these structures ; 

 at certain points on the surface of the sponge there is an agglomera- 

 tion of the syncytium into which there penetrates a number of long 

 spicules; this aggregated sarcode forms a small cylindrical body, 

 which gradually elongates ; the spicules already formed are displaced 

 by other fresh spicules ; the outgrowing filament, after having attained 

 a certain length, begins to form the bud at its tip (Figs. 9, 10, 11) ; 

 the peduncle has no canal and no j)ores, so that the bud cannot be 

 looked upon as being an invagination of the wall of the parent sj)ongo, 

 for the cavities which become developed in it arise indei^endently, 

 and have no connection with the cavity of the parent. 



General and Comparative Morphology of the Sponges. — To the 

 above paper is appended an abstract of M. Mereschk(nvsky's views on 

 this subject, in which he compares the sponges with the Hydroida. 



The formation of a very sim])le colony in the Hydroida is charac- 

 terized by the fact that tlie new individuals are not fortuitously 

 attached to the jjarent, but follow a rigorous law, so ordered that tho 

 appearance of one individual or tentacle is tho signal for the ajipear- 

 anco of lan identical one oi)posite to it ; after one pair has been 

 developed others may follow, but they arc always referable to the 

 formula 2 n. Nothing like this is to be observed in most sponges ; 

 the buds do not seem to folhnv any law, and arise without any order. 

 The second point of diflercnco is tliat in the Hydroida tho new 

 individuals or tentacles form a ramified colony, in which every indi- 

 vidual is completely distinct from its neighbours. Cases like this are 

 as a rare exception {Sycetta primitiva) to bo observed among sponges. 



