Notes on Zoothamnium Arbuscula. 



By James Spencer, F.R.M.S. 



(Read October 22, 18S6.J 



Plate I. 



All the members of the Club are no doubt more or less familiar 

 with the appearance of this organism, which bears a general 

 resemblance to a minute apple tree, with trunk, boughs, branches, 

 twigs, leaves, and fruit. Mr. Saville Kent, in his " Manual of the 

 Infusoria," says : — " Examined separately, each colony-stock may 

 be compared to a minute crystalline standard fruit tree, of which 

 the ordinary campanulate zooids may be likened to the leaves, and 

 the spheroidal or reproductive units to the fruit." The muscular 

 fibres all contract at the same time, and from time to time change 

 the appearance of the organism, from that of a tree into that of a 

 fluffy ball. I do not propose, however, to attempt to give any 

 complete description of the species, but merely to note some 

 observations of my own. 



The specimen which I observed was obtained by me at Walton- 

 on-Thames, on Saturday, the 11th of September, 1886, and was 

 attached to a rootlet of willow, on which there were besides some 

 sponges and other living organisms. It was placed in an observing 

 trough, holding half-a-pint of water brought from Walton. Its 

 natural size is shown in Plate 1, Fig. 1. In. Figures 2 and 3 are 

 sketches of it, x 10 diam., fully expanded and contracted, and 

 Fig. 4 is a drawing of a branch x 50 diam. I placed a microscope 

 in front of the tank, and gave the object an occasional look. I 

 noticed nothing particular till the following Tuesday morning, 

 when I saw upon the colony one fully-grown spheroidal zooid, and 

 eight others of various sizes, which afterwards became as large as 

 the first one. They were distributed pretty evenly about the 

 colony, and were in shape slightly prolate spheroids. I continued 

 my observations of these bodies from time to time as opportunities 

 offered themselves, and on the following Thursday morning found 

 that only eight remained, and that changes were taking place in 

 some of them. One had become shaped somewhat like a peg top 



