210 
Transactions of the 
TMonthly Microscopical 
L Journal, April 1, 1869. 
respect as in most osseous fishes. It is difficult, e, g., to teaze out 
the fihres in the centre of the lens of Anguilla acutirostris, but 
very easy to do so in the same part of Fetromyzon jiuviatilis ; and 
these two fishes are mentioned because I have often compared them 
as regards this point. Of the central part of the lens of the 
Lamprey, the fibres appear shorter, as might be expected, than those 
at its circumference ; and some of the central fibres, especially at 
the ends where they converge to the poles of the lens, are slightly 
jagged or sinuous at the edges, contrasting thus with the smooth- 
edged fibres of which by far the greater part of the lens is composed. 
The diameter of the fibres about their middle is nearly equal ; 
the smallest measure about go^o^ th, and the largest ^^^ih, while 
the prevailing diameter is -g-^,-th of an inch ; and the difference in 
the measurements would probably have been less had many bundles 
of the fibres been seen all lying fairly together on their flat surfaces. 
When the edge or thinner side presented well, it was found to be 
about -j-^-^ y th of an inch thick. 
The lens-fibres of the adult Lamprey are but little affected by 
various re-agents which act energetically on many other animal 
tissues. The ] ens-fibres retain their characters when treated either 
with strong acetic, sulphurous, strong nitric, dilute muriatic, or 
weak chromic acid ; but these fibres become more wavy and curled 
in acetic acid, and the same too in nitric acid, with the addition of 
a faint yellow tinge ; weak tannic acid clumps them together ; they 
become but slightly fainter with a solution either of caustic soda or 
ammonia; are but little affected by magenta and carmine; dyed 
yellow individually, orange-coloured in mass, and their edges made 
plainer by iodine ; and little changed by alcohol or sublimate. The 
immediate effects only of the forementioned re-agents were noticed 
on portions of the fibres separated under a deep object-glass. When 
boiled in water the lens becomes opaque, and its fibres may then be 
seen converging to points at its opposite poles ; in boiled fragments 
the fibres ap]Dear somewhat thickened and their hyaline character 
diminished (Fig. 2, from portions of the thickest fibres). 
Though the chemical properties of the lens are not very striking, 
their physical specialities are so beautifully distinct that they will 
probably be a good addition to the many examples now known of 
the value of several intimate or elementary structures of animals 
as diagnostic characters in systematic zoology. Upwards of a 
quarter of a century has passed since I proved, from a very exten- 
sive series of observations and in opposition to the then prevailing 
doctrine, that the structure of the red corpuscles of the blood affords 
a central diagnostic character between two great divisions — Pyrense- 
mata and Apyrensemata — of the vertebrate sub-kingdom ; and, in 
continuation of the same researches, it was shown that either the 
size or form of those corpuscles was sufficient alone to distinguish 
