Geneea of the isToKTH American Palaeozoic Bryozoa. 571 



tion takes place in the Bryozoa only in a single manner, by pro- 

 truding one of the walls of the mother cells and then partition- 

 ing off the protruded part, there are many different ways in 

 which gemmation has been observed to occur in corals. With 

 regard to the gemmation of Bryozoa very excellent observations 

 have been published by Barrois (Recherches sur I'embryologie 

 des Bryozoaires, Lille, 187T) Nitsche, Cla.pakede, etc. The mode 

 of gemmation of corals, on the other hand, has been studied in 

 detail by Koch, \vhose chief work on the subject has been pub- 

 lished in the Palaeontographica. (Ill Series, Vol. Y.) 



" The difference between the animals inhabiting the colonies of 

 Bryozoa and those that build up the colonies of corals are 

 extremely striking in many respects, and must find their expres- 

 sion also in the mode in which the colonies are built up. The 

 animals of the Bryozoa are, in the first place, much less long- 

 lived than those of the corals, as they show, for by far the largest 

 part of their existence, a so-called latent vitality. Each animal 

 of a colony of Bryozoa produces only one or two gems% only 

 exceptionally more, more or less simultaneously, and mostly 

 while it is yet in a rather juvenile stage, after which it stops its 

 functions in this direction. The animal of a colony of corals 

 never stops producing gems, but develops them at all times of its 

 life and at different levels. This difference alone is the cause of 

 a quite different growth of the colonies of the two classes of 

 animals. Whilst m the Bryozoa gems are produced only in the 

 peripheral parts of the colony, as for instance in j^ebenicea or 

 in arborescent forms only at the apex of the branches, as in 

 Entalophora, in the corals gems are produced all over the colony 

 in great numbers if the animals are well fed, etc., and in smaller 

 numbers if the contrary is the case. -^ * * ^ * 

 From all that we can gather in regard to the gemmation of 

 recent Bryozoa, it appears that besides having the gemmation 

 restricted to a very short period in a single animal's life, the 

 production of gems is restricted to one side of the animal. It is 

 always on the side opposite the aperture of the cell. This can be 

 very easily made out in the Cheilostomata, where the aperture is 

 always more or less lateral; but also in the CroL08TOMA.TA, where 



A word used by the author to express the product of gemmation. 



