ON BUDDING IN POLYZOA. 541 



of the adult. . . It loses no time, however, in developing 

 geminse, which soon change it to the compound form of the 

 adult" (p. 39). 



MetschnikofF (21) in his studies on Alcyone 11 a descrihes 

 the formation of the bud in the embryo. Allman in his Pre- 

 sidential Address to the Linnean Society (24) thus narrates it. 

 The segmentation of the egg produces " a central cavity sur- 

 rounded by a double layer of cells. This constitutes the cyst 

 of the well known Alcyonella -larva, within which two poly- 

 pides subsequently make their appearance by budding. In 

 this budding both lamina of the cyst-walls participate. The 

 outer lamina serves for the formation of the outer epithelium 

 of the tentacles, and the inner epithelium of the alimentary 

 canal ; while the central nervous system, which in the larva is 

 very large, is also most probably derived from it. The inner 

 lamina, on the other hand, forms all the muscles of the body, 

 as well as the genitalia and the inner epithelium of the body 

 cavity." 



Nitsche (22) has also studied the budding in Alcyonella 

 fungosa and in Cristate 11a mucedo. I again quote from 

 AUman's address, p. 499, " He (Nitsche) had already shown 

 that the wall of the cystid or zooecium of Alcyonella con- 

 sists of three diiferent layers besides the externally excreted 

 ectocyst or cuticula. These are an outer epithelium, an inner 

 epithelium, and a tunica muscularis lying between the two 

 and consisting of a structureless supporting membrane on 

 which lie transverse and longitudinal muscular fibres. The 

 first indication of the polypide-bud shows- itself as a sac-like 

 bulging inwards of the cystid wall. In this bulging the 

 tunica muscularis, however, takes no part, but seems to be 

 absorbed at the spot where the bud occurs. The polypide-bud 

 consists therefore at this stage of a two-layered cellular sac, 

 whose inner layer, bounding its central cavity, passes continu- 

 ously into the outer epithelium of the cystid wall, while the 

 outer layer is continuous with the inner epithelium of the 

 cystid. Nitsclie follows MetschnikofF in regarding the outer 

 epithelium of the cystid as the outer germinal layer or ecto- 



