Blood-corpuscles of A. tridactylum, &c. By Dr. Schmidt. 61 
to be diflferentiated from the rest of the body, forming a pellicle 
or membrane, though of no pronounced inner limitation, and un- 
distinguishable by the microscope. The latter is true with regard 
to the small, bi-concave blood-corpuscles of the Mammalia ; in the 
large, oval, nucleated corpuscles of the Amphibia, however, the 
pellicle, as we shall see hereafter, may he readily demonstrated. 
In the fresh blood of this class of animals we frequently meet with 
specimens of blood-corpuscles, on which, by a contraction of the 
protoplasm representing the greater portion of the whole body, 
the pellicle in question appears separated from the latter, thus 
manifesting its existence. Lankester himself mentions this fact 
(p. 368), and gives a representation of the specimens in Fig. 2, a. 
With due deference to the hypothesis of Bruecke, however, he calls 
the contracted protoplasm enclosing the nucleus, the zooid, and the 
separated enveloping pellicle, or membrane, the oikoid. Now, as 
far as I am able to understand the hypothesis of Bruecke, this 
oikoid represents a porous, transparent body ; and I can therefore 
not comprehend how Lankester can unite this idea of a porous 
substance, supposed to embrace the nucleus, and to determine the 
whole form of the blood-corpuscle, with that of his pellicle or 
membrane. The hypothesis of Bruecke, ingenious as it is, must 
eventually prove to be but an unsuccessful attempt to explain 
certain changes observed to occur in the form of the protoplasm 
of the coloured blood-corpuscle, which, after all, form the exceptions 
to the rule, and are such as may be readily explained without 
ascribing to this body a structure more complicated than can he 
demonstrated. 
A different view from the above is that entertained by Jas. G. 
Kichardson, of Philadelphia. He upholds the old theory, accord- 
ing to which the coloured blood-corpuscles of the Yertebrata are 
vesicles, each composed of a delicate, colourless, inelastic, porous, 
and perfectly flexible cell-wall, enclosing a coloured fluid, &c. To 
this conclusion Kichardson arrived, not only by his numerous ex- 
aminations of the blood-corpuscles of Man and other Mammalia, 
but also by the study of the corpuscles of the Menohranchus, which, 
with one exception, are the largest known. An interesting paper, 
containing these investigations, was republished in the July number, 
1871, of the ‘ Monthly Microscopical Journal.’ In it, he states 
that he twice succeeded in cutting a corpuscle in two with 
sharpened needles ; and that, on penetrating the vesicle with the 
edge of the needle, its contents were instantly evacuated, and dis- 
appeared at once in the surrounding fluid, while the cell-wall 
immediately shrunk together, and became twisted upon itself and 
around the nucleus into a perfectly hyaline particle. 
But while Kichardson maintains the true cell nature of the 
coloured blood-corpuscle, and adduced a number of observed facts 
