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SUMMARY OF CURRENT RESEARCHES RELATING TO 
and the thoracic-abdominal fold can soon be distinguished. The stomo- 
daeum is a tube which is bent forwards and flattened antero-posteriorly ; 
its wall consists of a single layer of cells ; it is surrounded by 
degenerating nuclei, yolk, and cells derived either from the abdominal 
plate or from the epiblast. The appendages are chiefly filled with yolk 
which is not absorbed until a comparatively late period. 
The spores form a marked characteristic of the early stages of the 
lobster, and throw light on similar bodies which have been observed in 
Alpheus and other Crustacea. They are small, deeply-staining masses 
of chromatin, and correspond to the granules or nucleoli of ordinary 
embryonic cells. It seems that we have here to do primarily with a 
remarkable case of cell-degeneration. The cells go to pieces, for some 
unknown reason, and the chromatin particles are gradually degraded 
into a substance resembling yolk. It is possible that these dissolving 
cells act as yolk-digesters. The spores disappear at a later stage, when 
five to six pairs of appendages are formed. The heart is represented by 
a space between the proximal end of the hind-gut and the body-wall ; 
this is filled with plasma, blood-corpuscles, and mesoderm cells, derived 
from the thoracic-abdominal process. 
In embryos of this stage there is a conspicuous circular patch of 
cells behind the heart, which probably represents one of the structures 
described under the name of “ dorsal organ.” The endoblast appears as 
a definite layer when eight to ten pairs of appendages are present ; its 
cells are derived from the yolk, and thus we see that it is not till a later 
stage that the germinal layers are established. In the egg-nauplius we 
can only recognize an ectoblast and an internal layer which consists of 
yolk-cells, proliferated ectoblast, and cells derived from the abdominal 
plate and mesoblast. The keel probably represents the endodermal disc 
of the Crayfish. The structure and development of the nervous system, 
fore and hind guts, and various organs seem, so far as they have been 
studied, to agree essentially with those of Alpheus. 
Developmental History of Brachyura.* — Mr. J. Lebedinski had for 
the chief object of his investigations Eriphya spinifrons ; the female of 
this crab carries a large number of eggs attached to the hairs of its 
abdominal appendages. The egg is about 0 • 5 mm. in diameter, and is 
quite spherical. It is invested by a chorion and a vitelline membrane. 
The earliest stage observed was that in which the already developed 
blastoderm covered only one pole ; at this stage some of the blasto- 
dermal cells unite to form a thick cylindrical epithelial germinal disc 
which gives rise to all three layers. The disc sinks down and exerts a 
mechanical compression on the underlying mesoendoderm ; this latter 
takes on a regular arrangement, for just below the cylindrical epithelium 
there is a row of elongated cells, internally to which there are amoeboid 
cells scattered in the yolk. The proliferating cells give rise to the 
ectoderm, the elongated to the mesoderm, and the amoeboid, which 
multiply actively, to the endoderm. 
While these processes are going on two new thickenings of the 
blastoderm are formed in front of, and independently of the disc ; these, 
which have a bilaterally symmetrical arrangement, are the cephalic 
Biol. Centralbl., x. (1890) pp. 178-85. 
