190 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 
Nervous system*— -This requires special methods and unusual pains in 
determining its histological character. I was the less unwilling to let 
this omission remain, because the nervous system of insects has been 
the subject of elaborate histological investigations on the part of Pro- 
fessor Leydig, 235 of Bonn, to whose work I may refer those who are de- 
sirous of further information on this subject. 
A recent article, by Hans Schultze, in vol. xvi, page 57, oftheArchiv 
fur mikroskopische Anatomic, is valuable. There is also an extensive 
memoir by K. B. Krieger, 236 on the nervous system of the crayfish, and 
another l>y Bell i' 17 on that of Squilla. 
Iu order, however, to illustrate the general structure of the nervous 
ganglia, I have given, in Fig. 11, a drawing of a section through the 
last abdominal ganglion of Caloptenus. The figure is somewhat dia- 
grammatic. A ganglion consists of two parts, the central fibrous por- 
tion, from which the nerves arise, and the peripheral layer of ganglion 
cells, GZ. On each side of these are two nerve roots, one the dorsal, DB, 
the other the ventral, VE. These Professor Semper, 233 in his article on 
Strobilation and segmentation, homologies with the roots of the spinal 
nerves in vertebrates, bul 1 do not know how far his conclusions on this 
point have been accepted by zoologists. It will be noticed that the four 
nerve roots in Fig. 11 pass out from the central fibrous mass, through 
the cellular layer, which latter is thus divided into four fields. 
The structure of the supraesophageal ganglion, the so-called brain, 
is very much more complicated in insects than was formerly supposed. 
It differs very essentially from any of the abdominal ganglia. The 
brain of insects has been recently investigated by Diet!, 239 Flogel, 240 and 
Newton. 241 
Graber: Ueber die tympanalen Sinnesorgane der Orthopteren. Denkschr. Wien. Akad., Bd. xxxvi, 
(1876), 2 abth., p. 1. 
: Ueber neue Otocystenartige Sinnesorgane der Insekten. Arch, fur miferos. Anat., Bd. xvi, 
p. 36 (1878). 
Mayer: Sopra certi organi di senso nelle antenne dei Ditteri. Mem. Reale Accad. dei Lincei. Roma, 4 
Maggio, 1879. (A criticism of Graber's paper on Otocysts.) 
Qrenacher: Untersuchungen iiber das Arthropodenange. KHnische Monatsblatter fur AugenheiL 
kunde, Jahrg. 15, Beilageheft zum Maiheft, 1877. 
Newton: Eye of Homarus. Quait. Journal Micros. Sci., 1875. 
Lowne: On the modification of the simple and compound eyes of Insects. Phil. Trans. R. Soc, London, 
voL 169, p. 577. 
Bullar: On the Development of the parasitic Isopoda. Phil. Trans. Roy. Soc, London, voL 169, p. 
513, 514 (structure of eye). 
Oraber : Ueber das unicorneale Tracheaten, und speciell des Arachnoideen- und Myriapodenauge. 
Arch. f. micros. Anat., xvii, p. 58 (1880). 
235 Vom Bau des Thierischen Kbrpers, Tubingen, 1864. Histologij des Nervensysteme der Arthropo. 
den, pp. 214-226 ; bei Orthopteren, p. 262. 
^Krieger: Ueber das Centralnervensystem des Flusskrebses. Zeitsch. f. wiss. Zool., xxxiii (1880), 
p. 527. Taf. xxxi-xxxiii. 
237 Bellonci, G. : Morfologia della systema nervose della Squilla mantis. Annali Museo civico stor. 
Nat. di Genova, vol. xii (1878), pp. 518-545. 
^Semper: Arbeitendes Zool. zoot. Inst., Wiirzburg, Bd. iii. 
239 Dietl: Die Organisation des Arthropodengehirns. Zeit. f. wiss. Zoologie, xxvii, p. 488. 
240 Flogel: Ueber den einheitlichen Bau des Gehirns in den verschiedenen Insectenordnungea. 
Zeitsch. f. wiss. Zool., Bd. xxx, Suppl. (1877), p. 556. 
241 E. T. Newton: On the brain of the cockroach, Blatta orientalis. Quatr. Jour. Micros. Sci., voL xix 
1879), p. 340. 
