598 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
B. esculenta. (4) The degree of development readied in a given time 
at a given temperature is very constant, but the differences induced by 
altered temperature are very marked. Thus, at the maximum tem- 
perature tadpoles may be hatched in six days, at 15° C. in about twenty- 
four days, and so on. (5) If the warmth-optimum is exceeded by even 
1°, abnormalities and death result. (6) The influence of temperature 
is primarily on the chemical processes, e.g. formation of nuclein sub- 
stances, and secondarily on the rate of cell-division. 
Experimental Embryology.* * * § — Herr Kaestner has made a number of 
experiments as to the effect a lowering of temperature has in interrupt- 
ing the incubation of hens’ eggs, and thereby inducing abnormalities. 
At all stages it is possible, by cooling below 28° C., to interrupt de- 
velopment without fatal influence. But the duration of non-fatal inter- 
ruption has its limits, varying with the temperature and with the stage 
of development. Thus, at 7° or so below the normal minimum of 28° C., 
the maximum of harmless interruption is 3 weeks at the beginning of 
the first stage of incubation, thereafter 6 days, after the sixth day 
72 hours, on the ninth day "iS hours, and thereafter about 24 hours. 
But further development after early interruption is apt to be attended 
with malformation. 
These malformations seem to be due to partial coalescence of the 
blastoderm and vitelline membrane, the yellow-yolk rising and pressing 
the blastoderm upwards. It is noteworthy that the disposition to 
malformations is restricted to interruptions in the first two days, and to 
conditions where the egg is kept horizontal. The malformations affect 
either the vitelline vascular system or the embryo. Those affecting the 
embryo may be (a) general, (Z>) local (influencing head, heart, or anterior 
amnion fold), (c) hydropic, or (d) of the nature of abnormal clefts in 
the medullary groove and the like. These malformations are generally 
irregular; only in certain cases can definite results be predicted from 
the conditions. 
Origin of Vertebrates.f — Dr. W. H. Gaskell took as the subject of 
his Presidential Address to the section of Physiology, at the British 
Association, the origin of Vertebrates, dealing apparently at greater 
length with the theory which he put before the Cambridge Physiological 
Society some months since.J Those who are inclined to accept the 
doctrine that the king-crab is the ancestor of the lamprey will find 
probably all the evidence that can be adduced in its favour in Dr. 
Gaskell’ s address. 
Structure and Development of the Vertebrate Kead.§ — Mr. W. A. 
Locy, in his present contribution to the structure and development of 
the vertebrate head, deals first with the metamerism of the head, and 
secondly with the sense-organs. A great amount of his investigation 
was carried on on Acantliias, while supplementary observations were 
made on a frog, a chick, and some other animals. He directs his 
special attention to the existence of what he calls neural segments. 
* Verb. Anat. Ges. X. Anat. Anzeig. Erg.-Heft, xii. (1896) pp. 136-45 (6 figs.). 
f Nature, liv. (1896) pp. 551-65 (9 figs.). 
X See this Journal, ante, p. 167. 
§ Journ. Morphol., xi. (1895) pp. 497-5S8 (5 pis.). 
