106 Transactions of the Royal Microscopical Society. 
forms by these means, I have produced them by the action of a 
very weak solution of chromic acid. But having, moreover, observed 
them naturally to occur in the fresh blood of the Frog, and also in 
that of a young Amphibia (Fig. 44), I have taken the view that 
the reagent plays only a subordinate part, as far as the production 
of these peculiar forms of blood-corpuscles is concerned ; they rather 
depend on a peculiar condition of the protoplasm, favouring the 
separation from the membraneous layer. And, indeed, the case 
appears to me so plain, that I can hardly conceive how it ever could 
have become a puzzle, even to some eminent histologists. For if 
we only imagine such a condition to exist throughout, where the 
protoplasm insensibly blends with the membraneous layer, and that at 
the same time a contraction of the protoplasm should take place, an 
entire separation of these two parts of the blood-corpuscle must 
evidently be the result. The protoplasm in such a case retracts 
upon the nucleus, which it completely surrounds, while the mem- 
braneous layer appears isolated, manifesting itself by a delicate 
double contour. And again, if the same process should take place 
without entirely separating the protoplasm from the membraneous 
layer, but leaving at certain small points a union between the two 
parts, the result must be the production of a number of filamentary 
processes, arising from the main bulk of the protoplasm and 
passing to those points of the membraneous layer. Of course, 
these processes are drawn out during the contraction of the proto- 
plasm (Fig. 44). In the fresh blood-corpuscles the contraction of 
the protoplasm must be attributed to natural though at the present 
time unknown causes. In those instances where the peculiar 
form of blood-corpuscles is produced by means of certain reagents, 
I suppose that a condition favouring the separation of the proto- 
plasm from the membraneous layer pre-exists, but that the con- 
traction of the former is called forth by the action of the particular 
reagent used. A representation of these star-like forms of blood- 
corpuscles artificially produced, and on a large scale, will be found in 
fig. 73, accompanying Kollett’s article “ On the Blood,” in Strieker’s 
‘ Handbuch der Lehre von den Geweben, &c.’ The double contour, 
representing the membraneous layer, seems to have been over- 
looked in this drawing. Fig. 57 of my own drawings repre- 
sents these forms on a smaller scale, produced on the coloured 
blood-corpuscles of the Tree-frog (Hyla) by the action of a very 
weak solution of chromic acid. At a the protoplasm has contracted 
in the form of a star, while the isolated membraneous layer mani- 
fests itself by a delicate double contour ; at h the processes of the 
protoplasm also have, by a continued action of the reagent, become 
separated from the membraneous layer, and retracted into the general 
mass of the protoplasm, covering the nucleus. 
Among the fresh blood-corpuscles of the Frog, still other forms 
