ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 575 



disturbance and injury. After rotation the centrifugal effects are seen in 

 a regular layered disposition of enchylema, thick amorphous plasma, and 

 yolk-plates. The cytoplasm must therefore be more or less fluid. If 

 there were a reticular meshwork between the yolk-plates there would be 

 traces of its disruption, but there are none. After the cytoplasm has 

 been resolved by centrifugal movement into its components, there is a 

 new organisation to a state like that of a yolk-free germinal disc, finely 

 alveolar in Butschli's sense. This structure cannot be the essentially 

 vital one — the indispensable physical architecture — for the experiments 

 show that it is the result of a still finer ultra-microscopic organisation. 



Formation of Centrosomes in Enucleated Egg-Fragments.* — 

 Naohide Yatsu has experimented with the eggs of the Nemertean, 

 ■Cerebratulus lacteus. When subjected to the action of a solution of 

 CaCl 2 , enucleated fragments of unfertilised eggs, obtained by cutting 

 the eggs singly at the metaphase of the first maturation mitosis, 

 develop true asters containing central bodies. The corresponding 

 nucleated fragments show the typical maturation spindle. Cytasters (i.e. 

 asters unconnected with nuclear matter) do not, however, appear in 

 enucleated fragments from unfertilised eggs before the fading of the 

 germinal vesicle. The central bodies of the cytasters developed in 

 enucleated fragments are centrioles identical in structure with those in 

 the nuclear asters of whole eggs similarly treated. Centrioles, therefore, 

 can be produced de novo in the matured cytoplasm, i.e. after the dissolu- 

 tion of the germinal vesicle. 



^ v 



Ovum of Lamprey.f — W. Lubosch has made a detailed study of the 

 ovum of Petromyzon planer i, with especial reference to the formation of 

 yolk, the egg-envelopes (vitelline membrane or oolemma and zona 

 pellucida or radiata), the follicular epithelium and its metamorphosis, 

 the theca folliculi, the germinal vesicle, and its changes. His observa- 

 tions on the role the follicular epithelium plays in yolk-formation and 

 its final disappearance by a sort of inflammation are of great interest. 

 In regard to the maturation, it is noted that it differs markedly from that 

 in Amphibians, Selachians, and Teleosts. It is more like that of many 

 invertebrates. The directive chromosomes arise from a large unified 

 nucleolus. 



Passage of the Mammalian Ovum into the Fallopian Tube. % — 

 Ulrich Gerhardt discusses numerous concrete cases, and points out that 

 there are several different ways in which the passage of the ovum into 

 the tube is secured. The simplest is an enlargement of the receptive 

 surface, the infundibulum tubae, in proportion to the ovary. This is 

 seen in Monotremes, Marsupials, and Cetaceans. The second and most 

 frequent arrangement is that a portion of the peritoneum of the tube is 

 utilised as a common envelope for infundibulum and ovary, forming a 

 bursa ovarii, as in Insectivora, Chiroptera, Artiodactvla, Rodents, and 

 Carnivora. A third method seems to be confined to the horse, and 

 depends on a reduction of the ovulating surface in proportion to the in- 



• Journ. Exp. Zool„ ii. (1905) pp. 287-312 (8 figs.). ■ 



t Jenaische Zeitschr. Naturwiss., xxxviii. (1904) pp. 673-724 (1 pi., 4 figs.). 

 JIOp. cit., xxxix. (1905) pp. 649-712 (33 fige.). 



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