STRUCTURE OF THE SPERMATOZOON OF THE NEWT. 253 
do not find it so ultra minute as I at first thought it. It is indeed 
of very appreciable magnitude, being in breadth about 1.5 micras 
(0.0015 mm.), and in length 2.0 micras (0.002 mm.), though 
obviously accurate measurements of such objects are difficult, for 
to detect the actual termination of an impalpably fine point is not 
always possible.* 
Such a determinate and remarkable structure as that here des- 
cribed cannot be supposed to exist without some purposed recent 
researches at once suggest that this is to attach the spermatozoon to, 
and enable it to penetrate into the ovum in the early stages of fer- 
tilisation, as has been shown to occur by Fol and others ; and we 
should expect to find a similar formation in other spermatozoa. In 
those, however, which I have hitherto examined I have not detected 
it, and the structure of many, as that of the toad, and of most 
mammalia, does not appear to admit of its existence. 
To prepare the spermatozoa for the examination of this object 
the first essential is to get them as nearly as possible in contact 
with the cover-glass and flat upon it; this requires some care, to 
avoid their drying, by which they are materially altered. They may 
be preserved by several methods, either by treating for twelve to 
twenty-four hours with a concentrated solution of picric acid, a 
dilute solution of chromic acid, by Dr. Klein’s method with a five 
per cent. solution of ammonium chromate, by iodine, by silver 
nitrate, or by osmic acid or gold chloride ; the latter are convenient 
as being quicker. I have myself most usually employed picric 
acid. For staining I have found glycerine magentay{ the best 
method, as it stains all parts as strongly as desired. ‘To show the 
general structure alcoholic carminate of ammonia is the most satis- 
factory, but it does not stain the barb deeply. Other aniline dyes 
I have not found answer so well. If it be intended to examine the 
preparation with a homogeneous, or “ oil” immersion objective, it 
should be mounted in Canada: balsam, the objective having, as is 
generally known, no advantage, and, indeed, being inferior to dry 
*JTn such measurements I have found great advantage in the use of a cob- 
web micrometer, admirably constructed by Messrs. Ross, which has the second 
web, which is usually fixed, movable; this both saves time and promotes 
accuracy, as in the usual form (with only one web movable) it is almost im- 
possible, by means of the mechanical stage, to bring an object into exact con- 
tact with the fixed web, which is done at once with ease and certainty by the 
second movable one. Having now used this a good deal, I certainly prefer it 
to any other plan; whatever arrangement is adopted, however, it is necessary to 
determine the value of the scale of the eye-piece with a stage micrometer, as the 
least variation in the conditions of the instrument, as e.g., slightly turning the 
screw collar of the objective, appreciably alters their relations. 
+ Magenta cryst., I part; glycerine, 200 parts; alcohol, 150 parts; aq., 150 
parts; immerse the preparation in the solution for from two to four minutes 
according to the depth of colouring required, and then wash. 
