608 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
chromatin threads are longitudinally split, transverse division and 
normal disposition of eight segments take place — all quite regularly. 
As division is accomplished the daughter-nucleus of cell A stains some- 
what differently from that of cell B. 
The second division of cell A is very different, as it occurs after the 
fashion which Flemming has called heterotypic. In each of the two 
derivatives of A there are only four chromatin loops. There is a 
“reduction-division.” The two daughter-nuclei pass into the middle of 
the yolk and remain there in vesicular form throughout the whole of the 
embryonic development. They are the genital cells. 
The B cell is intruded among the marginal cells of the future 
blastopore. It begins to divide by normal mitoses but with very broad 
dyaster-figures. Its derivatives form the primary mesoblasts. The 
formation of the gastrula is then described. Apart from the primary 
mesoblasts and the primary endoderm cells (corner-cells of the gastrula- 
mouth, pole-cells of the endoderm) mitoses never occur in this stage, 
either in ectoderm, or endoderm, or genital cells. 
The gastrulation in Cyclops is the subject of special discussion. Of 
much importance is the early differentiation of a few primitive cells 
or pole-cells giving origin to endoderm, mesoderm, and genital rudiment. 
The endoderm arises by a succession of divisions in a few superficial 
pole -cells, which, with nuclear spindles directed obliquely to the radius 
of the ovum, give off internally successive crops of endoderm cells. 
These broaden out in a cup, but do not multiply internally until the 
midgut is definitely formed. Perhaps the form of gastrula may be 
directly connected with the early concentration of those elements 
which have the power of originating endoderm. Dr. Hacker suggests 
a possible line of evolution from multipolar immigration, through 
delamination and polar proliferation, to the concentrated type of 
endoderm-formation in Cyclops , viz. with a few pole-cells and a resulting 
cupola-like gastrula. 
The fate of the second polar body is still obscure. It wanders 
into the centre of the embryo, and seems to come into relation with 
the derivative of the A cell. Perhaps there is some strange quasi- 
sexual attraction between them. Dr. Hacker concludes his paper with 
a further discussion of the heterotypic division of the A cell. 
The Genus Miracia.* — Prof. C. Claus has studied this remarkable 
genus with especial reference to the structure of its eye. Dana gave a 
general description, and Brady described the appendages ; Claus goes 
into greater detail. The cuticle is traversed by fine pores arranged in 
groups — the openings of unicellular skin-glands. Besides these there 
are canals from which very delicate, perhaps tactile, cuticular structures 
protrude. The anterior antennae correspond accurately to those of 
Harpactidae ; the posterior antennae have a basal piece which Brady 
overlooked ; the oral appendages most nearly resemble those of Setella , 
and the reduction of the palp -appendages is characteristic. Prof. Claus 
has various additions to make to Brady’s account of the other 
appendages. 
The gut is relatively wide, and bears internally projecting cells ; the 
Arbeit. Zool. Inst. Univ. Wien (Claus), ix. (1891) pp. 267-84 (3 pis.). 
