572 Report of the State Geologist. 



the aperture is terminal, the apex always bends to one side, oppo- 

 site to the side on which the gems are produced. We will call 

 the gem-producing side the dorsal one. In creeping colonies this 

 dorsal side is always turned downwards ; in arborescent forms it 

 is turned inward, toward the axis of the stem. If thus a creeping 

 colony changes into an arborescent one, the animals must turn 

 around to a certain extent to bring their dorsal sides into a 

 fitting position, but that is all the change that takes place in such 

 a case. 



" In the corals, on the contrary, gemmation takes place, indis- 

 criminately, on all sides of the animal, and, therefore, no lineal 

 descent of the animals is observable. 



" In the Monticqlipoeid^ propagation takes place in a way which 

 deviates very far from the modes described in the Bryozoa. As 

 in corals two essentially different modes of propagation are 

 observable — gemmation and fissiparity. The first of these is the 

 more common one, and, therefore, we shall consider it first in the 

 MoNTicuLiPOEiDJi:. If we turn to Prof. Kooh's extremely impor- 

 tant * paper on the propagation of corals, we find he does not 

 retain the old opinion as to the essential difference between fissi- 

 parity and gemmation, and from a biological point of view such 

 an opinion may not be entirely justifiable, but from a practical 



point of view it appears to us as of great importance. 



* * * -x- * * *'* * 



" The four modes of gemmation are classed by Koch in the 

 following manner : 



" A. Internal gemmation. 



'* a. Tabular gemmation-; the young coralites are produced by 

 means of singularly transformed tabulaB. 



"This mode of gemmation chiefly occurs in the Eugosa or 

 Tetracoralla. 



" B. External gemmation. 



" a. Intermural gemmation ; the young corallites are produced by 

 the splitting of the primary mural plate (or primordial wall) of two 

 or more adjoining corallites. 



"6. Coenenchymal gemmation; young corallites are produced 

 by the fusion of several interstitial tubes. 



" c, Stolonal gemmation ; young corallites are produced "by the 

 budding of one of the stolons. 



