322 The American Naturalist. [April 
the very assumption of this office, they ultimately become waste 
material and as such pass away from the system. 
One of the most interesting of the many problems that, even 
in these few experiments, have presented themselves, remains 
as yet unsolved. Owing to want of time the ultimate fate of 
the carbon contained in the spleen-pulp cells remains unascer- 
tained, nor can any suggestions be offered. Only after more 
prolonged experiments could it be determined whether the 
carbon disappeared from the cells or remained permanently in 
them. After the determination of this point if the first condi- 
tion was found to obtain, the question as to the method of this 
removal would remain to be settled. In all the problems con- 
nected with the blood and circulation this perplexing organ 
seems to play an important part and when, setting aside func- 
tion, differences of opinion exist as to structure, it can easily be 
seen that discussion dn this part of the experiments involves 
doubtful and difficult problems. As is usual in any investiga- 
tion many doubtful points have been raised that yet await 
settlement, leaving an interesting and fruitful field for further 
work. s 
Notr.—The author wishes to express her indebtedness to the American Micro- 
_ scopical Society for the use of plates illustrating this article. i 
Prate IV. 
Leucocytes. 
A. Group of carbon-laden leucocytes showing amoeboid phases. 
a. b. Leucocytes of Necturus. 
n. Nucleus. 
p. Cell-body. 
c. d. Leucocytes of Cryptobranchus. 
n. Nucleus. 
p. Cell-body. 
Drawn from dried preparations. 
B. Group of Leucocytes, showing amoeboid cell-bodi 
amoeboid nuclei. 
a. b. c. Leucocytes of Necturus. 
n. Nucleus. 
p. Cell-body. 
es and 
