go THE NORTHERN MICROSCOPIST. 
arrangement of the gonidial cells. In the non-gelatinous plants, 
the green cells are generally free, but in many of the Collemas, 
they are joined together in a moniliform manner, or in the fashion 
of beads on a string. In some members of the family they are 
diffused through the thallus, while in a few others they are grouped 
into small series of cells. 
( Zo be concluded in our next.) 
OUR BOOK SHELF. 
A Biological Atlas. D. M‘Atpine, F.C.S., etc, and A. N. 
M‘ALPINE, B.Sc. Edinburgh and London: W. & A. K. 
Johnston. 1880. 423 colored figures and diagrams, and 49 pages 
of text. 
It has been our aim in previous numbers of this Journal to point 
out to the possessors of microscopes how good and profitable work 
may be done with them, and instead of ranging over the whole 
field of microscopy, how we may become useful in our generation 
by settling down to the serious study of one or two particular 
branches. 
There is no reason why anyone should not become generally 
acquainted with nearly every branch of microscopy, but he will find 
it almost impossible to go into the details of each department ; as 
the practical work required in such a case would be simply 
enormous. There is no doubt that the mere student is often 
perplexed as to what subject he shall pursue, and if a theme of no 
great difficulty were presented to him, with an outline of the 
manner in which it should be performed, a long road into the 
mysteries of this fascinating science would be opened up. 
The above sentiment induces us to introduce to the favourable 
notice of our readers the foregoing Biological Atlas which has been 
sent us for review. Its price is low and the whole matter so pre- 
eminently practical that even the veriest tyro should find no 
difficulty in understanding it. The subjects are arranged in the 
order of gradually increasing development and consequent difficulty. 
The plates are colored, which not merely adds to the scenic effect, 
but enables one to see at a glance what the diagram is intended to 
ex hibit. 
Take for instance Plate III. whereon are delineated Protococcus 
pluvialis and P. vulgaris—there is the resting spore of this latter — 
species showing in a very clear manner the cell-wall and the 
chlorophyll-containing protoplasm. By the side of this is figured 
