A STANDARD SIZE OF BODY TUBE. 203 
great if they will only adopt the same vigorous methods of seeking 
them. 
In looking for specimens of microscopic aquatic life it is necessary 
to note carefully the conditions which prove most favourable to their 
existence, for it is certain that the larger our acquaintance with 
them the more sure are we of success, and the less likely are we to 
become tired of the pursuit before we have mastered its difficulties. 
The water needs to be fairly still for most things, and I have 
found it most favourable when there is some clay and a fair quantity 
of vegetable matter in suspension ; but a few creatures, as Hydra 
vulgaris and some species of Polyzoa, being voracious feeders, are 
usually most abundant where the water is in rapid motion, as at the 
flood-gates and outlets of pools, the weeds, woodwork, or stones in 
these parts being sometimes truly carpeted with these animals. 
( Zo be continued. ) 
A STANDARD SIZE OF BODY TUBE. 
S we wish all microscopists to notice the various sizes of body 
tubes in the market we shall continue to insert the following 
table for several more numbers :— 
Diameter of Ocular. 
Name of Vendor or 
Description of Model. Body. Neck. 
Maker. Se 
inches & 64ths | inches & 64ths 
Powell & Lealand..| Large Stand......... 1°234-64 58-64 
i & Jy Becks s.- National: Stosess.: 1°17-64 57-64 
smith & Beck...::. Large stand ......... 1°I7-64 56-64 
Hoss; 62° COs <c2ea Ross-Jackson ...... 1°20-64 57-64 
Ditto! see Ross-Zentmayer ...| 1°20-64 57-64 
Waneer.. 22.2 ee Earpe stand «.. ....<. 1°I7-64 57-64 
Browsing... i525. Ordinary stand..... 1°17-64 54-64 
DWH seecvosece oe saee ae Challense 22352252. 1°13-64 56-64 
Collins feo Ie. Plate yeas ooetie. dees 1°17-64 
Crouch. Avie Lee: IPFeMmier fr..0.. 1.2. I'14-64 54-64 
Pieylward) 2.250.020. Workings: ft. 2.655. 1°23-64 56-64 
iParkesm eo. fo. 0c Students ese.) ci 0. 1° 7-64 % 
PISSe hoes ae ws Ordiagty 5..2.2.2..+. 58-64 i 
SU eee ere Wrecowe 2h: 59-64 = 
Pngelbert ic :42.5.. Petar! Sc. 1°6-64 s 
_ Upon those stands marked with an asterisk the camera-lucida 
is not made to fit in the ordinary way. 
