160 HYATT, 



Thus the adherence of the endocyst to the ectocyst, and 

 the adherence of the latter to the surface, both depend 

 upon the gelatinous nature of the ectocyst, which, as we 

 have just seen, is characteristic of varieties in Fredericella 

 of some species in Plumatella, and of the genus in Pectiu- 

 atella and Cristatella. 



Natural position erect or horizontal. The single col- 

 onies in any species of Fredericella are as apt to have 

 free and erect branches, as to have them wholly attached 

 and horizontal. The free branches, however, are rarely 

 seen in Plumatella arethusa, and I have not observed 

 them in P. diffusa, vesicularis, and vitrea, though it is 

 quite probable that they may be found more or less in the 

 brown variety of P. diffusa. They are also, doubtless, 

 found in P. nitida, which is a luxuriant growth. 



Lophopus, both in this country and in Europe, is erect. 

 Pectinatella and Cristatella are invariably horizontal. 

 The position of the branches is therefore of generic value 

 in the last three genera, and of variable value in Frederi- 

 cella and Plumatella. 



Branching. I have not yet found an adult colony 

 without branches either in Fredericella or Plumatella. 

 There are, however, very few branches on the colonies of 

 variety b of Plumatella vitrea. 



Although the number of branches and branchlets in 

 the two lower genera are often less, they are, in the ma- 

 jority of the full-grown individuals, more numerous, 

 amounting in some specimens of P. Arethusa, P. diffusa, 

 and P. vesicularis to over fifty ; and in variety c, of Fred- 

 ericella Regina and P. Arethusa, they probably reach 

 hundreds. 



The lobes of Pectinatella rarely exceed ten, with about 

 two or three branchlets to each, making in all thirty 

 branches large and small. 



The indefinite multiplication of the branches in Pec- 

 tinatella is prevented by the frequency of self-division, 

 which limits the size of the colonies, while greatly in- 

 creasing their number. In Cristatella this characteristic 

 disappears. 



