328 THE AMERICAN NATURALIST; [Vor. XXXIV. 
* 
Sense Organs of Nereis. — F. E. Langdon! has described three 
kinds of sense organs in the skin of JVzreis virens Sars. The diffuse 
sense organs consist of groups. of bipolar nerve cells whose bodies 
form a part of the external epidermis, whose peripheral ends extend 
as sense bristles into the surrounding water, and whose central pro- 
jections are in the form of nerve fibres terminating probably as peri- 
cellular nerve baskets around ganglion cells in the central nervous 
organs. The diffuse sense organs are most numerous in those parts of 
the body most exposed to contact, and represent organs for mechani- 
cal and possibly chemical stimulation. The prostomium possesses 
an anterior and a posterior pair of cephalic organs, each of which 
consists of a group of bipolar cells whose peripheral processes end 
in the epidermis, and whose central processes terminate in the brain. 
The anterior pair differ from the posterior in that their cell bodies 
lie between epidermis and brain instead of in the brain. The third 
class of organs consists of groups of spirally arranged cells, hence 
called spiral organs. The central processes from these organs take 
a direction appropriate for nerve fibres, but have not been traced 
into nervous organs. Their function as epidermal eyes is, therefore, 
hypothetical. P. 
Breeding Infusoria. — As bearing upon the problem of death it 
is interesting to note that the doctor's thesis of Dimitri Jonkowsky’ 
records some partial repetition of Maupas's famous work upon 
Infusoria. Maupas found degeneration and death befell many 
Infusoria when they were bred for many generations without conju- 
gating, but that the change in the nuclear machinery that takes 
place in conjugation would start another long series of generations. 
That degeneration is necessary without such renewal seems less 
probable from the experiment of the present author, though his evi- 
dence is not conclusive. In the case of FPleurotricha lanceolata 
(Ehbg.) 458 generations were reared in eight months and yet no 
degeneration was found, except in a few cases in the last generation. 
He suggests the rapidity with which the animals breed, which was 
greater in Maupas's experiments, may be a factor in the occurrence 
of degeneration. Bearing in mind the sensitiveness of many Infuso- 
ria to the chemical and physical nature of the liquid they are reared 
in, it seems not unlikely that degeneration may depend upon other 
1 Langdon, F. E. The Sense Organs of Nereis virens, Sars. The Journ. of 
Comp. Neurology, vol. x, No. 1, pp. 1-77, Pls. I-III, 1900. 
2 Verh. des Naturhist. med. Verlins zu Heidelberg, Bd. vi, 1898. 
