748 The American Naturalist. [August, 
Contrary to what would be expected the optic nerve fibres seem to 
grow out from the brain toward the ommatidia of the eye 
While the author supports the view that the rows of nerve-cord 
forming cells in insects are homologous with the neural cell-rows of 
annelids (especially since they are most clearly shown in the oldest 
winged insects, the Orthoptera) he recognizes the possibility of this 
being merely a case of precocious segregation 
Another interesting part of the paper denis with the formation of 
the gonads and the'sexual ducts. 
The mesoderm is early split up into eighteen pairs of blocks, which 
become hollow and extend from the region of the definitive mouth to 
that of the definitive anus, the length of the blastopore. Two pairs 
correspond to the second and the third division of the brain, the others 
are in the thorax and abdomen. The first pair send out hollow diverti- 
cula into the antenne; those back of the head send diverticula into 
the limbs. 
In the walls of these hollow mesodermal sacs on the side next the 
median plane and the yolk, certain large cells become recognizable as 
the germ cells. These cells are formed, however, in the abdomen in 
the first to the sixth segments. They are of mesodermal origin, appar- 
ently, and first recognized when thus distributed in segmentally 
arranged clusters in the walls of the mesodermal sacs. In one abnor- 
mal case such germ cells occurred also in the tenth abdominal segment. 
These germ cells fall into the cavities of the mesodermal sacs and 
multiply by caryokinetic division, The six successive masses of germ 
cells become connected into one ovary or one testis by the outgrowths 
of solid diverticula from each sac to the one anterior to it and subse- 
quent fusion. 
The sexual ducts arise also from these mesodermal sacs. Thus, 
while in the head and thorax the diverticula that go to the limbs are 
converted into their muscles, the diverticula in the abdomen either dis- 
appear along with the transitory appendages or else remain as parts 
of the sexual ducts. In the male the mesodermal diverticula of the 
the terminal part of the sperm duct. 
The rest of the duct is formed from a solid ridge on the inner wall of 
the mesodermal sacs between the tenth segment and the anterior six 
forming the testis. The ducts then may he TO as hollow out- 
growths of the ceelomic sacs, I are in the 
seventh segment, but at the same time there is a pair in the tenth. 
While the former become the oviducts, the latter, representing the ter- 
minal — of the sperm ducts, ultimately disappear. With the 
