134 
Bibliographical Notices. 
colours, as, for example, the Plumularia falcata, which produces some 
white and some yellow. The number produced varies according to 
the species, nor does it seem to be uniform even in the same species. 
After moving about in the open waters for some hours, not by cilia 
but by inherent mobility, the planule rests and settles on some fixed 
body, where it contracts itself into a circular spot, whence the young 
polypidom speedily shoots up in the shape of a primary spine. We 
quote the author’s description of the planules of Sertulariapolyzonias : 
“ About fifty planules issued from the vesicles on the 8th of 
July, the specimens having been procured on the day preceding. 
These animals were nearly a third of a line in length ; the body 
plump, approaching rotundity, somewhat flattened below, of a 
smooth uniform aspect, and darker in colour than straw-yellow. In 
course of their escape they were obviously suspended from various 
parts of the specimen by an invisible thread ; but when reaching any 
solid surface they advanced with an equal, gliding motion, resembling 
that of Plana7'ice. The observer could not associate them with any 
other genus in the ‘ Systema Naturae.’ No external organs could be 
detected by the most careful microscopical inspection. They as- 
sumed various forms, according to circumstances, and, as afterwards 
established, these were modified also, according to the period of their 
existence. 
** Many planulae continued quitting the vesicles from the 8th 
until the 12th of July. They spread on the bottom and crowded 
together on the sides of their vessels. Numerous dark green, thick, 
obtuse spines were rising from spots on the bottom on the 14th of 
the month. Several were enlarging as buds next day, which had 
developed as a hydra from some others of them.” (p. 146.) 
These discoveries in the embryology of zoophytes will necessitate 
some alterations in their systematical distribution, and will, we are 
inclined to think, lead ultimately to the recognition of new principles 
on which to found even their distribution into new classes. 
The book is full of particulars relative to the growth, the almost 
unlimited regerminations, the structure and physiology and the 
habits of zoophytes, but the interest lies rather in the minutiae and 
truth of the details than in general deductions, and cannot be relished 
unless by a student who will read them seriously and in earnest and 
in the spirit in which they are written, for the style is unfortunately 
sometimes ambiguous and obscure, and too often Johnsonian with- 
out the Johnsonian antithesis and elegance. We shall therefore pass 
on to particularize the species described, making a remark or two as 
the occasion arises. 
1. Tuhularia indivisa. This is described and illustrated with mi- 
nute detail, and is evidently a favourite. The experiments made to 
test its tenacity of life and its regenerative powers remind us of 
those made by Trembley and Baker on the Hydrse, and they are 
equally remarkable, but to detail them would be endless, for, as the 
author tells us, “ no definite rules or principles can anticipate the 
precise course of reproduction,” p. 28. Sections of a single stalk 
will each of them produce a new head, more especially the section 
