GOO SUMMARY OF CURRENT RESEARCHES RELATING; TO 



time, and in order to prevent maceration it lias to be rehardened 

 from time to time. Eggs heated with Perenyi's fluid gavo the most 

 satisfactory sections. 



The egg when laid is surrounded by a tough chorion (deposited 

 during the passage down the oviduct) which is covered with granules. 

 Within this is a structureless vitelline membrane formed whilst the 

 egg is still in the ovary. 



In the centro of the egg is the nucleus surrounded by nearly 

 clear protoplasm ; this is connected by protoplasmic strands with a 

 peripheral layer of protoplasm — the blastema — containing numerous 

 oil-globules ; imbedded in the meshes of the protoplasmic network 

 connecting the two layers of protoplasm are numerous large albuminoid 

 yolk-corpuscles. 



2. The embryo. — The development of the embryo is, for conveni- 

 ence, divided into five periods. 



The prcbladodermic period. — The yolk shrinks from the vitelline 

 membrane, and the space thus formed is filled with pervitelline 

 liquid. In this condition one side — the future ventral plate — is flat, 

 the other convex. The contraction of the yolk causes the blastema to 

 be moulded on the underlying yolk-corpuscles, so as to mark out the 

 surface of the egg into polygonal areas. The central nucleus divides 

 up, and the nuclei thus formed, together with corresponding portions 

 of protoplasm, migrate to the surface and enter the blastema ; and 

 thus this layer becomes converted into a series of nucleated cells — the 

 blastoderm. 



The second period includes the changes up to the first appearance 

 of the appendages. The irregular cells of the blastoderm divide up 

 and give rise to regular cells. In one instance the author observed 

 a depression at one pole of the egg, similar to that described by 

 Salensky as an invagination ; but Locy is uncertain as to what really 

 happens, and considers it to have some relation to the primitive 

 cumulus. This latter structure is a thickening of the blastoderm at 

 one end of the ventral surface. At the opjiosite end a caudal thicken- 

 ing appears, and between the two is the ventral plate. This is 

 soon marked by transverse furrows into " protozonites." These 

 extend laterally for about a quarter of the circumference of the egg, 

 whilst the series of seven or eight zonites occupy about two-thirds the 

 circumference. The blastoderm along the ventral surface is more 

 than one cell layer thick, whereas dorsally there is a single layer of 

 flattened cells. When the protozonites are formed, both ectoderm 

 and mesoderm are distinguishable ; the former as a layer of regular, 

 columnar cells ; the latter of cuboidal cells not so definitely arranged. 



The third period extends from the appearance of the appendages to 

 the time of reversion. 



Six protozonites are distinguishable ; these soon become rounded 

 at their lateral extremities and project as bud-like processes — the 

 appendages. The first two zonites are formed from the cephalic 

 plate ; new ones are added from the caudal plate. The four next 

 zonites appear, and have small rounded prominences upon them — the 

 provisional mesosomatic appendages. The prusomatic appendages 



