No. 3-] DEVELOPMENT OF MARLXE SPONGES. 365 



coast) have demonstrated that small pieces or cuttings of the 

 commercial sponge have the ability to reproduce the entire 

 organism. Cuttings from Tedania, which were suspended from 

 mangrove roots in one of the "sounds" of Green Turtle Cay, 

 grew very perceptibly in a month. 



In Tethya and Tetilla (Selenka 29, Deszo 3, 4) external 

 buds are produced in a curious way. The buds consist of a 

 solid mass of cells, and are formed in the peripheral region of 

 the mother beneath the skin. As they mature they are 

 gradually pushed out of the body along the spicules of the 

 mother, until their only connection with the parent is through 

 a slender stalk made up chiefly of these spicules. The bud 

 then drops off. Deszo's account of the early formation of 

 these structures is extremely interesting, although his recorded 

 facts scarcely seem to warrant his inferences. According to 

 Deszo, the bud or gemmule is derived from a single cell, 

 which undergoes a segmentation, and growing all the while 

 gives rise to a solid morula. By the time the original cell has 

 divided into four, a differentiation of " germ layers " takes 

 place : one of the four cells constitutes the entoderm, the 

 remaining three the ectoderm. The ectoderm then grows 

 entirely round the entoderm cell. Cell multiplication con- 

 tinues, the primary entoderm cell producing a solid mass of 

 entoderm, surrounded by a single layer of ectoderm cells. 

 The latter layer then splits off from its inner surface a layer 

 of mesoderm, and itself gives rise to the external epithelium 

 of the mature bud and to a stratum of tissue just beneath the 

 epithelium, in which small asters (spicules) are developed. 

 Deszo's interpretation of certain cells as constituting distinct 

 germ layers, is not very strongly supported by his figures. 

 Vosmaer's criticism in regard to this point may be given : " Es 

 ist wohl klar dass fiir die Deutungen der Zellen, wie sie Deszo 

 vornimmt, kein Grund vorliegt " (Bronn's Class, und Ordnung, 

 p. 427). Deszo points out the importance, from a biological 

 standpoint, of the discovery of germ layers in a non-sexually 

 produced embryo, and calls to mind a similar discovery by 

 Oscar Schmidt in the developing buds of Loxosoma. Schmidt's 

 account of the development of the Loxosoma buds (23, 24), 



