226 



HYATT, 



FIG. 18. 



hood of Philadelphia by Dr. Leidy, is found also near 

 Cambridge, Mass., and in Sebago Lake, Maine. 



The colonies differ considerably. Variety a, found 

 upon smooth boards in Spy Pond near Cambridge, is very 

 large when full grown, the branches 

 often crowded, but never adherent, 

 the cells distinct. The branches, how- 

 ever, of variety b, upon rougher 

 boards, where the decaying surface 

 was deeply grooved, grew in these channels, and were 

 neither so radiatory or closely crowded. These are 

 only accidental varieties, which do not differ essentially 

 in structure ; but at White's Bridge, Sebago Lake, Maine, 

 I found upon the same colony an interesting structural 

 variation from the usual mode of building out the 

 branches. The tip of a branch (Fig. 18), either in con- 

 sequence of some impediment upon the surface, or from 

 a sudden and excessive development of the vital energies, 

 began to produce three buds at a time instead of one, 

 thus giving to the branch a lobiform aspect corresponding 

 with the characters of variety b of Plumatella vitrea. 



This species may therefore be assumed to be capable 

 of two important variations, one in which the cells are 

 distinct, and one (variety c) in which they are partly 

 merged in the branch. The ectocyst is not constantly 

 colorless, but may be brown in some localities. 



b d a a a c c 



3.5 3 9x10 8.5x9 



FIG. 19, a, a, a, front, back, and side views of one statoblast; c, c, front and back 

 views of another specimen, both from Beaver Pond, near Cambridge, Mass.; d, 

 from Spy Pondf near same place ; b, from Sebago Lake, Maine, is inaccurate, 

 should be but little longer than d, and about the same thickness. 



The anal extremity of the intestine is rather lower than 

 in P. Arethusa, and the gastric ccecum is very blunt. 

 Posterior retentors are about eight rows, and the anterior 

 retentors about ten or twelve bands ; tentacles, fifty to 



