28 ARACHNIDA. 



statements as to the development of Chdifer up to the time of the formation of 

 the blastoderm are, indeed, confirmed by Steckeb with regard to Chthonius, 

 but the description of the latter author is not calculated to inspire confidence. 

 A more recent treatise by J. Barrois * on the ontogeny of Chdifer is too short 

 to supply many further details. 



The eggs of Chdifer and of Chthonius are spherical and crowded 

 with yolk-spherules. Each is surrounded by a vitelline membrane, 

 and again by a second envelope probably secreted by the oviduct. 

 These eggs are carried by the mother on the ventral surface of the 

 abdomen, where they pass through their development. The cleavage 

 is at first complete, the egg dividing up into two, four, and eight 

 equal blastomeres (Fig. 15 A). In the latter stage, i.e., when the 

 egg is divided up into eight spheres, clear protoplasmic segments 

 are said to appear on the surface of the yolk-laden spheres. The 

 number of these clear cells soon greatly increases, until they form a 

 layer surrounding a central mass of yolk (Fig. 15 B); this layer may 

 be regarded as the blastoderm. The large yolk-segments with their 

 nuclei can still be clearly seen within the egg.f 



The whole process must, no doubt, be thus explained : The few nuclei which 

 enabled the yolk to break up into segments, by division, send off nuclei to the 

 periphery, the nuclei which remain within corresponding to the yolk-nuclei of 

 other Arthropod eggs. In the fact that the yolk itself remains segmented these 

 forms are peculiar. 



As the segmentation of the yolk gradually disappears, the blasto- 

 derm divides into an outer and an inner layer of cells (Metschnikoff, 

 Fig. 15 C). About this time, large clear bodies appear between the 

 blastoderm and the egg - integument ; these contain structures 

 resembling nuclei, and therefore resemble cells (Fig. 15 C). 

 Metschnikoff was reminded by them of an embryonic envelope, but 

 could not convince himself that such a covering was actually present, 

 and regarded these structures as disintegrated masses of albumen, a 

 view also taken by Stecker. These cells recall those found beneath 

 the cuticular envelopes in the Mites (Claparede's haemamoebae, 

 Fig. 53, p. 99). 



* We have not heard of any more detailed work on this subject by Barrois ; 

 Stecker's preliminary notice also seems not to have been followed by any 

 larger treatise. [See Barrois (App. to Lit. on Pseudoscorpiones, No. I.). — Ed.] 



t [Barrois (App. to Lit. on Pseudoscorpiones, No. I.) has recently very fully 

 investigated the development of Chdifer; he finds that segmentation may be 

 either total or partial, the latter condition predominating and resulting in a core 

 of yolk with peripheral cells, some large, which form the blastoderm, others very 

 small, which become applied to the vitelline membrane. A deep median ventral 

 longitudinal groove appears, from the walls of which mesoderm-cells are pro- 

 liferated off. Origin of the entoderm obscure, nuclei appear in the yolk. — Ed.] 



