ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
201 
A comparison of the various modes of yolk-cleavage in Insects leads 
the author to believe that, in the great majority, there is a partial centro- 
lecithal segmentation. After this true cleavage is ended there may be 
a secondary fragmentation of the nutrient yolk. Primitively the 
Insect’s egg was proportionately very poor in yolk and segmentation 
was total, as it is to-day in the Poduridae. 
In the cleavage of certain eggs there are formed cells or nuclei 
which do not range themselves in the germinal layers ; these may he 
collectively known as the parablast ; it consists of non-specialized cells 
and may be of different significance in different animals, and it is not 
necessary to suppose that it is always present. There is no doubt that 
those tissues which in some animals are of parablastic origin are in others 
derived from the germinal layers. The parablast is chiefly found in 
meroblastic ova. 
Development of Female Reproductive Organs of the Cockroach.* 
— Dr. R. Ileymons has studied this in Phyllodromia ( Blatta ) germanica 
L. In early stages of development, some mesoderm cells become 
genital cells, and after the formation of the coelom sacs more meso- 
derm cells, which form an epithelial sheath around part of the coelome, 
are similarly modified. Thus the origin of the genital cells is essen- 
tially the same as in Annelids, and it is likely that in all insects tho 
genital cells have this mesoderinic origin. The terminal thread is 
important only during embryonic and larval life, during which it has to 
do with the changes in the position of the ovaries. In the cockroach 
the genital cells and the epithelial cells of the ovaries arc from the first 
independent. Isolated genital cells appear in the blastoderm long 
before there is any connected genital rudiment associated with epithelial 
cells. When the genital cells migrate to the dorsal walls of the primi- 
tive segments, then for the first time epithelial cells become associated 
with them. During the whole of development the two sets of cells are 
distinct, even in the terminal chambers of the ovarian tubes. So far as 
in higher insects “indifferent cells” really occur in the terminal cham- 
bers, it is simply due to the fact that the differentiation of mesoderm 
cells into genital and epithelial, which occurs very early in tho cock- 
roach, is of late occurrence in these other insects. 
Digestive Canal of Orthoptera.f — Si g. O. Visart has studied the 
mid-gut (meso-intestine) of Acridium, CEdipoda, and other Orthoptera. 
In the epithelium there are cylindrical cells with a border, much 
elongated clavate cells without a border, and quite distinct large oval 
cells. The cylindrical cells represent the quiescent stage of the very 
actively secretory elongated cells. The same two types occur in the 
glandular caeca. A careful description of the border or plateau of the 
cylindrical cells is given. In the clavate glandular cells the nuclear 
division is amitotic and of the nature of fragmentation. In the secre- 
tory process the nucleus sometimes remains apparently indifferent and 
basal in position ; but when there is a supplementary anterior nucleus it 
undergoes chromatolysis and is dissolved in the secretory “ gemmation.” 
The same cell may exhibit secretory gemmation several times. Sorne- 
* Zeitschr. f. Wiss. Zool., liii. (1891) pp. 431-536 (3 pis.). 
f Atti Soe. Tosc. Sci. Nat., vii. (1891) pp. 277-85. 
