508 SUMMAEY OF CURKENT RESEARCHES RELATING TO 



outline and then disappears, its contents becoming fused with, and in- 

 distinguishable from, the cell-substance. As the ovary is full of 

 spermatozoa the ova are probably fertilized in it. They thence make 

 their way into the uterus. The youngest uterine ovum observed had no 

 nucleus ; a small spindle appears at one point at the periphery of the egg, 

 and a male pronucleus is present at the opposite side. The spindle 

 divides twice to form polar bodies, and the remainiler of the spindle 

 remained as the female pronucleus : it lies at a little distance from the 

 surface, and is lobed. The male pronucleus is large and rounded ; the 

 two probably conjugate, though this has not been observed. The re- 

 sulting nucleus passes to the periphery ; it is large and lobed, and soon 

 becomes surrounded by a large mass of dense protoplasm. 



An account is also given of the maturation of the ovum in P. Novse- 

 Zealandise, which differs not inconsiderably from that of the Cape 

 species ; for example, spermatozoa are present in the receptacula seminis 

 and not in the ovary ; the nucleus is at one period vacuolate, and no 

 polar bodies have as yet been observed. 



In conclusion some general remarks are made on the origin of the 

 ova from germinal epithelium, the disappearance of the germinal vesicle, 

 the formation of the polar bodies, and the formation of the yolk. As to 

 the last question ; while it has been suggested that the yolk arises in 

 the protoplasm of the egg itself, from the breaking up of the germinal 

 vesicle, or from the follicle cells, it is of interest to observe that 

 P. Novse-Zealandise not only affords an example of all these three 

 methods, but also a fourth, for the yolk arise.-; from yolk which is present 

 in the ovary itself. Miss Sheldon does not think she could have failed 

 to see polar bodies in P. Novse-Zealandise had they been formed, and 

 she thinks that their absence in that species and their presence in the 

 Cape species can only be explained by supposing that they are in some 

 way dependent on the yolk, since in it lies the main difference between 

 the eggs. If this be so, it is clear the polar bodies cannot have the 

 significance which Weismann attributes to them, and in any case the 

 similarity between the two polar bodies in the Cape species is not what 

 we should have expected if their meaning were so different as Weismann 

 suggests. 



S. Arachnida. 



Life-Mstories of Glyciphagus domesticus and G. spinipes.* — Mr. 

 A. D. Michael finds that there is a hypopial stage in the life-history of 

 GlycipJiagi, just as there is in that of Tyroglyphus, but it is far less 

 developed, and is not, so far as is known, an active stage. At present 

 we do not know whether it occurs in all species, but we do know that it 

 does not occur in the life of every individual of a species. The stage 

 is not the result of desiccation and other unfavourable circumstances, 

 but occurs as often under favourable conditions. In the species inves- 

 tigated it occupies the period between the penultimate ecdysis and that 

 immediately previous. 



In G. sjnnipes the Hypopus is fully armed, and capable of moving its 

 legs, but not of walking or other active movement ; as a rule, it does 

 not leave the skin of the young nymph within which it is formed ; the 

 more adult nymph is formed within the Hypopus while the latter is still 

 within the young nymphal skin. In G. domesticus the hypopial stage is 



* Journ. Linn. Soc. Lond., xx. (1889) pp. 285-98 (1 pi.). 



