7GC SUMMARY OF CURRENT RESEARCHES RELATING TO 



vitelline sac of birds by happening to discover in the peritoneal cavity 

 of young pigeons a soft yellowish mass which appeared to bo a foreign 

 body. In the pigeon the vitelline pedicle atrophies before birth, 

 and the cord undergoes torsion, and soon becomes obliterated ; about 

 a month after the young leave the egg the pedicle breaks and the 

 sacs becomo free. Later on it forms adhesions with the viscera, 

 becomes enveloped by vessels and is completely absorbed. In the 

 chick and the duck the vitelline pedicle persists, and as it shortens it 

 draws the sac with it; the latter never becomes free ; it is rapidly 

 absorbed. It would appear that the absorption of yolk is most active 

 in those which lead a free life on leaving the egg. The author gives 

 a detailed account of the changes which occur in the pigeon. 



Oviposition in Phyllomedusa.* — Dr. H. v. Ihering finds that 

 Phyllomedusa Iheringii lays its eggs, not in water, but on the over- 

 hanging leaves ; the masses of eggs are wrapped between two leaves, 

 in such a way as to leave an opening only below. He thinks that 

 the tailed larva; drop into the water; but owing to the drying uj> of 

 the leaves, he was unable to follow the development of the eggs. 

 This mode of oviposition constitutes a passage to that of Uylodes, in 

 which the whole development takes place in the air. 



Mr. G. A. Boulenger, in some remarks upon Dr. von Ihering's 

 note, refers to the arboreal frog, Chiromantis rufescens, belonging to 

 the family Kanidaa, which, though widely remote from Phyllomedusa, 

 lays its eggs in a similar way. Mr. Boulenger gives a useful 

 synoptic table, showing the facts known as to the mode in which the 

 Anura deposit or protect their offspring. 



Influence of Variations in the Physico-Chemical Medium on the 

 Development of Animals. f — M. E. Yung gives the results of 

 numerous experiments made by him upon tadpoles under various 

 conditions. 



The fewer tadpoles there are in a given quantity of water, in 

 otherwise similar conditions, the sooner do they develope into young 

 frogs. Tadpoles develope more quickly in a shallow and wide vessel 

 of water than in a narrower and deeper vessel. This is partly due 

 to the greater aeration of the water, and partly to the less distance 

 to be traversed in order to reach the surface. The author discusses 

 the influence that food has upon the sexuality of the animal, and 

 after citing several writers, gives his opinion that unisexual forms 

 are derived from hermaphrodite ancestors. He refers to the various 

 opinions as to the time at which the indifferent genital organ of the 

 embryo takes on its male or female character, as a result of the 

 development of the one kind of cell and the disappearance of the 

 opposite kind in the gonad. As a rule, in a given number of eggs 

 only a slightly greater percentage of females are developed, but this 

 number can be increased by feeding the tadpoles with meat, and still 

 more so by means of a fish diet. 



* Ann. nnd Mag. Nat. Hist., xvii. (18SG) pp. 4C1-4. 

 f Anh. Sci. Phys. et Nat., xiv. (18S5) pp. 502-22. 



