HYATT, OBSERVATIONS ON POLYZOA. 193 



X. Observations on Polyzoa. Suborder Phyiactolcemata. 

 BY ALPHEUS HYATT. 



[Continued from page 160.] 

 C(EN(ECIAL BEANCHES. 



Diffuse or adherent. Variety b, of Fredericella Wal- 

 cottii, has its branches closer together than variety a of 

 the same species ; but the only specimens yet described, 

 either in this country or in Europe, that have crowded 

 branches, are those belonging to variety c, of Fredericella 

 regina. 



Among these, a branch may occasionally become ad- 

 herent for a short space. This, however, rarely occurs, 

 and seems to be Avholly accidental. The diffusion of the 

 branches is the ordinary character of Plumatella, but in 

 four of the five American species, the crowded Alcyonel- 

 loid variety is developed more or less, according to the 

 locality in which the species lives. I have been unable to 

 determine whether the crowding of the branches takes place 

 by the direct action of physical causes or not. In some 

 cases the area of attachment would seem to be the only 

 assignable cause, as in P. vesicularis, where the tip of 

 a branch assumes the Alcyonelloid character by being 

 crowded upon the edge of a projecting branch,* but the 

 same variety in P. vitrea grows upon the smooth surface 

 of a piece of tin. In P. Arethusa and F. regina, found 

 in Tommy's Brook, near Gorham, Me., the current 

 seemed to be in some way connected with the production 

 of the Alcyonelloid variety ; but the same varieties of the 

 three other species of this genus developed profusely in 

 the brackish and still water of Mystic Pond ; upon broad 

 surfaces of attachment in the still fresh water of Spy 

 Pond, and in a small artificial lake on Mr. John Hop- 

 kins' estate near Baltimore. In fact, there is no uniformity 

 in their mode of occurrence, the same form often appearr 

 ing under the most diverse circumstances. The quantity 

 of food may possibly influence their growth, though with 

 regard to this I have collected no reliable data. 



* See description of species. 



COMMUNICATIONS ESSEX INSTITUTE, VOL. V. 26 JAN., 1868. 



