836 THE AMERICAN NATURALIST. (VoL. XXXIII. 
In addition to the somites represented by the compound eyes and the 
antennz, many Collembola possess rudimentary intercalary append- 
ages, indicating a third premandibular somite. The remaining somites 
are represented by the mandibles, the superlingue, the first maxille, 
and the labium. At an early stage these seven somites have each a 
pair of ganglia; the three pairs of premandibular ganglia unite to 
form the supracesophageal ganglion, and the remaining four pairs 
fuse to form the subcesophageal ganglion. A comparison of the 
hexapod and crustacean head is shown as follows: — 
SOMITE. HEXAPODA. CRUSTACEA» 
I Compound Eyes Compound Eyes 
2 Antenne Antennules 
3 ener Appendages Antenne 
4 Mandible Mandibles 
5 doaar First Maxillæ 
6 First Maxillæ Second Maxillæ 
7 Labium First Maxillipedes 
G: Hi, f: 
The optic nerves of amphibians, according to the researches of 
Fritz,’ undergo a total crossing in the chiasma, so that all the fibres 
from one eye pass to the other side of the brain. The chiasma has 
the form of interwoven bundles, which in the Urodela are larger 
- in the middle of the nerves and smaller dorsally and ventrally, and in 
the Anura are larger ventrally and smaller dorsally. The chiasma 
has relatively few glia cells compared with the optic nerve. The 
courses of the nerve fibres in the chiasma were demonstrated by 
ordinary histological methods and degeneration experiments. Four 
weeks after the extirpation of an eye the optic nerve fibres began to 
show the first evidences of degeneration, a condition obtained in 
warm-blooded animals in two days. In seven months after the 
removal of the eye the severed nerve had entirely disappeared. 
The process of absorption which accompanies the degeneration of 
the nerves in Amphibia makes the degeneration method much less 
satisfactory for these animals than for other vertebrates. G yy p, 
Notes. — The few Ophidian tapeworms heretofore known have 
been supplemented by the discovery of a new species, /chthyotenia 
1 Fritz, F. Ueber die Struktur des Chiasma nervorum opticorum bei Amphi- 
bien, Jena. Zeitschr. für Naturwissenschaften, Bd. xxxiii, pp. 191-262, Taf. VI-XI. 
1899. 
