ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 463 



at critical stages, such as gastrulatiou, concrescence, head differentiation, 

 the establishment of the circulation. These crises probably represent 

 the apices of curves of morphogenetic activity, when the metabolic 

 rhythm is at its height. A lowering of the rate of metabolism affects 

 these processes more profoundly than it would processes associated with 

 a low developmental tonus. 



Many cases of independently differentiating tissues were observed, 

 cnief among which are chromatophores, heart, and fins. These structures 

 continue to develop when isolated from their normal environment. De- 

 differentiation of the more highly differentiated parts occurs readily 

 even while the less differentiated parts continue to grow. General 

 death occurs slowly, and some tissues are particularly resistant. Chro- 

 matophores go on to their definitive state even when the tissues of 

 the embryonic body are reduced to a generalized mass of cells. 



Behaviour of Chromatin in Teleost Hybrids.* — Margaret Morris 

 finds that in the cross Fundulus (female) and Ctenolabrus (male) the 

 germ-nuclei are closely applied to each other, but form chromosomes 

 for the first division without having fused. The chromosomes of the 

 first cleavage spindle are of two types, which correspond respectively to 

 those seen in the normally fertilized eggs of the two species. Although 

 the foreign chromosomes lag somewhat behind the others in going to 

 the poles, they are all finally included in the daughter-nuclei of the two- 

 cell stage. The two types of chromosomes reappear in the spindle of 

 the second cleavage, and can be distinguished throughout the develop- 

 ment, which was followed as far as the twelve-hour stage. In the twelve- 

 hour stage large cells with irregular nuclei are found, which represent the 

 beginning of disturbances, which afterwards lead to the abnormality or 

 death of the larvae. There was no evidence of elimination of the 

 paternal chromatin at any stage. 



b. Histology. 



Independent Life of Cells. t — S. von Schumacher gives an account 

 of some of the recent work on the independent life and individuality 

 of cells. Although division of labour has occurred in Metazoa, there 

 is often a considerable retention of autonomy. The power of inde- 

 pendent life is most marked in cells which live in fluid media, such 

 as the spermatozoa and the leucocytes. The spermatozoa received by a 

 queen bee from the drone may live in the receptaculum seminis for at 

 least three years. The spermatozoa of the salamander may live for two 

 years in Siebold's sacs, blind diverticula of the cloacal wall of the female. 

 The spermatozoa of the bat remain in the uterus of the female from 

 autumn to spring, when fertilization occurs. Grosser found the uterus 

 of Vesperugo noctula full of sperms at the end of August. Human 

 spermatozoa may survive for eight and a half days, and those of the 

 guinea-pig for eleven days, in a refrigerator. 



* Journ. Exper. Zool., xvi. (1914) pp. 501-21 (5 pis.). 



t Die Individualist der Zelle. Jena, 1914, pp. 1-12. (Heft 10, vol. ii. of 

 Sammlung Anat. Physiol. Yortrage, ed. by Gaupp and Trendelenburg.) 



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