366 WILSON. [Vol. IX. 



however, has not been confirmed by later investigators. On 

 the contrary Seeliger finds that the bud is not derived from a 

 single cell, but is formed in a very different way. According 

 to Seeliger (30, 31) the bud, both in Lo.xosoma and Pedicellina, 

 is formed as a papilla of the body wall (or stolon, in the case 

 of Pedicellina), an invagination at the end of the papilla giving 

 rise to the atrium and alimentary tract. The mesoderm of the 

 bud is derived from the mesoderm of the parent, the ectoderm 

 of the bud is derived from the ectoderm of the parent; and the 

 only new formation is the entoderm, which is produced by an 

 invagination of the adult ectoderm. Seeliger's account destroys 

 the possibility of drawing a parallel between sponge gemmules, 

 which develop germ layers, and the buds of Loxosoma. 



The internal buds or gemmules of the fresh-water sponges 

 have been known since the time of Linnasus, but their precise 

 origin is still open to discussion. 



The ripe gemmule consists of a solid mass of polygonal 

 cells, full of yolk, surrounded by a complex capsule. The 

 capsule is perforated by an opening (hilum), through which 

 in the spring the cellular mass creeps out, developing into a 

 new sponge. The capsule is composed of an inner and outer 

 cuticular layer, between which is a layer containing skeletal 

 elements (amphidisks or other spicules). According to Gotte 

 (6), all the cells in a particular region of the body of the 

 parent sponge, not only those of the mesoderm, but those of 

 the flagellated chambers and canals as well, become trans- 

 formed into a mass of yolk-containing cells, which constitutes 

 the gemmule. According to Marshall (19), however, the gem- 

 mule is formed exclusively from an aggregation of mesoderm 

 cells. In whichever way formed, the young gemmule becomes 

 differentiated into two layers, an inner mass of larger cells full 

 of yolk, and a peripheral layer of cells (Gdtte). According to 

 Gotte, the peripheral layer of cells secretes the inner and 

 outer cuticle, and gives rise to the amphidisks. According to 

 Wierzejski (cited from Vosmaer 33, p. 429), the peripheral layer 

 assumes the character of a columnar epithelium. Between it 

 and the central mass appears the inner cuticular layer. The 

 spicules and amphidisks are formed entirely outside the gem- 



