5. Entwicklungslehre. 573 



Hyperopisus bebe) erinnert. Jürgens ist im Zweite!, ob bei Polyccntnis 

 Schomburgkii wirklich eine Brutpflege, d. b. Bewachung durcb die Alten, 

 stattfindet Wolterstorff (Magdeburg). 



1204) Gtlaesner, L. (Zool. Institut Strasburg i. E.), Die Gastrulation 



von Petromyzon und die .,Concrescene"-Frage. 



(Zool. Anz. 85,23. p. 728-733. 2 Fig. 1910.) 

 Polemischen Inhaltes, Ablehnung der Konkreszenzlehre. 



Gutherz (Berlin). 



1205) Eyelesliynier, A. C. and J. 31. Wilson (St. Louis Univ.), Nor- 

 mal Plates of the development of Necturus maculosus. EL 11 der 

 Normentafeln zur Entwicklungsgeschichte der Wirbeltiere, herausgegeben von 

 F. Keibel. 4°. 50 S. 3 Tafeln. Jena 1910. 



In der üblichen tabellarischen Weise stellen die amerikanischen Autoren 

 die Entwicklung von Necturus dar. Bemerkenswert sind die Angaben über 

 die Variabilität der Entwicklung sowohl der äußeren Formen alsderinneren 

 Organanlagen. Die Tafeln sind mustergültig ausgeführt. Po 11 (Berlin). 



1206) Steinbeil (Sitz.-Ber. „Isis", 3Iünchen), Jugendform von Tropi- 

 donotus natrix var. astreptophorus. 



(Blätter f. Aquar.- u. Terrarienkunde 21,10. p. 159. 1910.) 

 Das Jugendkleid dieser Schlange, der spanischen Varietät der Ringel- 

 natter, weicht (wenigstens in der ersten Zeit nach dem Ausschlüpfen) völlig 

 vom Alterskleide ab, entgegen der Angabe von Dürigen zum Beispiel. 



Wolterstorff (Magdeburg). 



1207) Tims, H. W. M. (London üniversity), Seal Embryos. 

 (National Antarctic Expedition 1901—4 [Natural History] 5. p. 1—21. 2 Plates. 



London, British Museum. 1910.) 



An anatomical description of twenty-nine embryos of Leptonychotes 

 Weddelli, ranging from 12 mm in length to a foetus almost ready for birth. 

 The following points are of biological interest. 



The foetal hair is thick and woolly, and is not cast of until two weeks 

 after birth, during which time the young lies on the ice. In Phoca on the 

 contrary the foetal hair is shed in utero, and the young enter the water 

 immediately. 



A vestige of an external ear is found in very early embryos, closely 

 similar to that described by Howes in the cetacea. 



The limbs are at first at right angles to the body, but very early undergo 

 flexure so as to lie quite parallel with its length. 



The digits are webbed from their origin, and in early foetuses have 

 relatively large nails. 



The most remarkable point in the skeleton is the great flexure of the 

 vertebral column in the cervical region, by which the length of the neck is 

 reduced. The vertebral centra are brought close to the ventral body-wall, 

 pushing the Oesophagus and trac one side. This eurvature is found in 



both sexes; it is present in the young foetus and becomes accentuated with 

 increasing age. 



The condition of the teeth indicated thal many of the deeiduous teeth 

 do not develop beyond a non-ealeified enamel organ, and disappear at an 

 earlier age than is usually supposed. Traces of three apper incisors were 

 found. 



