234 SI MMARY. OF CUBEENT RESEARCHES RELATING TO 



Bancroft raised a tadpole through metamorphosis, and found ova in 

 the gonads. 



In the chapter on early stages in development, the author outlines 

 the view that the formation of soap-like substances induces streaming 

 phenomena which lead to cleavage. It may be that a positive chemo- 

 tropism of the blastomeres toward oxygen leads to the formation of 

 the blastula. It is noted that it has not been proved for animals that 

 the spermatozoon is chemotactically attracted to the ovum. In the 

 chapter on fertilization and oxidation it is noted that oxygen is 

 necessary for nuclear or cell division, including maturation of the ovum 

 and the germination of seeds. The entrance of the spermatozoon 

 accelerates the processes of oxidation and other reactions, e.g. hydrolyses, 

 which can proceed independently of oxidations. 



In succeeding chapters the author discusses early observations on 

 natural parthenogenesis in insects, the history of the earlier experiments 

 on aitificial parthenogenesis, the methods of artificial parthenogenesis, 

 ih«' effect of artificial membrane formation, the action of the hypertonic 

 solution after membrane formation, the fertilizing effect of foreign 

 blood and foreign cell extracts, the action of the spermatozoon, 

 artificial parthenogenesis and heredity, and similar subjects. 



The last question discussed is whether an embryo can develop from 

 a spermatozoon. J. de Meyer placed the spermatozoa of Echinus 

 microtuberculatus in sea-water containing an extract of the eggs of the 

 same species and found that they swelled up. Loeb and Bancroft put 

 the spermatozoa of the fowl in nutritive media and saw the formation 

 of a vesicle around the head of the spermatozoon. In yolk and white 

 of egg the spermatozoon seems to undergo transformation into a 

 nucleus, but no mitoses or aster formation was observed. 



Chemistry of Development.* — R. A. Gortner has made comparative 

 analyses of the eggs and the newly hatched larvae of the giant 

 salamander, Cryptobranchus alleganiensis. The total dry weight 

 diminishes by 1*6 p.c, due to loss of carbon-dioxide and water, for 

 the total nitrogen does not change. There is a gain of fats to the 

 extent of 14 p.c. over that in the egg. The greatest loss is from the 

 protein fraction, some of which has gone into the fat. 



There is considerable evidence that the nitrogen ratios in the 

 protein fraction are not fixed quantities, but that some amino-acids are 

 more necessary than others for the developing embryos. There is 

 probably a continuous breaking down and recombining of the resulting 

 radicals into new compounds. 



It seems probable that there is, in the eggs of Cryptobranchus, a 

 carbohydrate nucleus, either free (glycogen) or combined in the form of 

 a glycoprotein, and that during the process of embryonic growth this 

 carbohydrate is broken down to carbon-dioxide and water, with a 

 consequent liberation of energy for the work of development. But the 

 breaking down of the carbohydrate proceeds more rapidly than the 

 needs of growth demand, with the result that the surplus energy is 

 stored as fat. 



* Year-book, Carnegie Inst. Washington, xiii. (1914) pp. 122-3. 



