NAIS. 131 
smooth and cylindrical, the portion behind it provided with a double 
row of thin tufts or prickles, some of them composed of several bristles. 
The extremities contain the mouth, and the termination of the excre- 
tory canal. 
In some a yellow globule is seen, towards the anterior, and in one 
or two white spherules have appeared. 
The mouth seems a dilateable cylinder, without a proboscis. The 
food may be the minute Entomostraca, as a specimen of the Cypris ap- 
peared in the intestine. This last organ is of variable form, being 
divided into several sacs, of alterable appearance and numbers. 
The transparence of the animal completely exposes the internal con- 
formation. 
M. Duges affirms that propagation takes place by means of ova or 
capsules, and that he has witnessed redintegration of the animal after 
being sundered transversely. 
It dwells among the roots of the Iris and Equisetum, not very far 
from the surface of lakes and ponds. Owing to its impatience of exposure 
to the light, it is somewhat difficult to obtain delineations of any speci- 
men. 
Puate XVII. 
Fie. 1. Nais lacustris. 
2. The same, enlarged. 
3. The same, more enlarged. 
4. Another specimen, shewing the internal organization, enlarged. 
5. Another specimen, shewing a different appearance in the internal 
organization, enlarged. 
§ 2. NAIs pROBOSCIDEAA—Plate XVII. Figs. 6, 7. 
Length nine lines ; body very slender, slightly flattened throughout, 
the anterior prolonged into a very flexible process, terminating in a 
point ; the posterior extremity obtuse. Near the origin of the probosci- 
dal process is a small jet-black eye, on each side of the head, at some dis- 
