1891.] Embryology. 283 
yolk-cells in the center of the egg have their nuclei undergo a process 
of fragmentation, increasing by direct development. The germ-cells 
(sexual cells) appear when there is but a single-layered blastoderm. 
few of the blastoderm cells, which later form the sexual cells, enlarge 
and form a group of cells which push beneath the surface. The 
epithelium of the midgut forms from entoderm cells. The nuclei of 
the yolk-cells form many small nuclei, surrounded by a quantity of 
plasma: lying between the yolk and mesoderm, and soon arrange 
themselves into the cylindrical epithelium of the midgut. The author 
points out the correspondence between the early stages of Phalangium 
and Limulus. 
The Embryology of a Scorpion:—Malcolm Laurie publishes 
a paper under the above title.‘ The earliest. stage observed had a 
small blastoderm at the surface of one end of the egg. This becomes 
several layered by a process resembling delamination. At a later stage 
there is asingle outer row of cells over one end of the egg, and a thick- 
ened mass of cells beneath, some of which are migrating into the 
yolk. The presence of a primitive groove is doubtful. At the 
posterior end of the blastoderm there is formed a mass of hypo- 
blast cells, and these may represent invaginated hypoblast. Later a 
layer of primitive hypoblast cells is to be found under the rest of the 
blastoderm, and seems to be simply ‘‘sp#¢’’ from the epiblast, 
Numerous cells migrate into the yolk. The mesoblast forms under 
the whole ventral plate from a multiplication of cells of the primitive 
hypoblast. The origin of the serous membrane and, the amnion is 
described in detail. Ccelomic spaces form in the mesoblast of the 
segments, and the thoracic appendages contaif portions of the ccelom. 
The coxal glands open at the base of the fifth appendages, and are at 
first a pair of simple tubes, opening exteriorly at one end and into the 
cœlom at the other. They seem to be homologous with nephridia. 
The lateral eyes are as Lankester and Bourne affirmed, monostichous. 
The central eyes arise by invagination. The stomodzum forms early ; 
the proctodæum much later as a solid plug of cells. The gill-books 
are appendages comparable to the abdominal appendages of Limulus. 
Development of the Fresh-Water Sponge.*® — Dr. . Otto 
Mass has studied the development from the egg of Spongilla. The first 
two segments are equal in size and structure, and similarly the 4, 8, and 
16 segments, are all alike, giving similar reactions to staining reagents. 
* Quart. Jour. Micro. Sci., Vol. XXXI., Pt. II. 
* Zeit. f. wiss. Zool., Band so, Heft 4. 
