184 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 Sertularia polyzonias : 



" 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 Planarice. 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 planulse 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. Tubularia 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 Hydrae, 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 



