Über eine spontane Extrasystolie im Schrittmachersystem des Tunicatenherzens (Ciona intestinalis L.)

Summary Some experimental results on action potential (EKG) in the pacemaker system of the tunicata heart (Ciona intestinalis) are presented. Synchronous records of both end and central heart regions show a spontaneous chance of the electrical activity in the middle of the heart tube, just before the periodic reversal of the direction of the pulsating wave starts. Extra systoles in the central pacemaker influence the terminal centres and provoke reversal.

---

---

Herrn Prof.W. v. Buddenbrock zum 80. Geburtstag.     

A light and electron microscope study of spherical structures in the test cells of an ascidianCiona intestinalis L.

Summary Spherical structures in the test cells that surround the embryos of the ascidianCiona intestinalis L. (Tunicata, phylum Chordata) were studied by both light and electron microscope. Our data support the view that these structures are microorganism-like cells living in symbiosis with the test cells. Their possible role is discussed.Acknowledgment. The authors are indebted to the Institute of Comparative Anatomy of Palermo for the use of the Zeiss EM 9 Electron Microscope. Particular thanks to Mr Salvatore Bucculeri for his technical assistance.     

Hypoxia as a negative reinforcing stimulus in the squirrel monkey

Summary Squirrel monkeys learned to avoid hypoxia by pressing a bar. Each bar-press replaced the noxious gas mixture with normal air for 3 sec. The data further indicated that O₂ itself has no positive reinforcing effect.     

Efficacy of ethanol as a discriminative stimulus in ethanol-preferring and ethanol-nonpreferring rats

Rats which exhibited a preference for drinking a 6% w/v solution of ethanol in a free choice situation did not differ in their sensitivity to ethanol from animals exhibiting an aversion for ethanol, as measured by leaning rates in a T-maze task in which ethanol served as a discriminative stimulus.     

Efficacy of ethanol as a discriminative stimulus in ethanol-preferring and ethanol-nonpreferring rats

Summary Rats which exhibited a preference for drinking a 6% w/v solution of ethanol in a free choice situation did not differ in their sensitivity to ethanol from animals exhibiting an aversion for ethanol, as measured by learning rates in a T-maze task in which ethanol served as a discriminative stimulus.The author is thankful to Miss Christine Currey for technical assistance.     

The effect of cardiac glycoside storage on growth rate and adult size in the butterflyDanaus chrysippus (L.)

Summary Danaus chrysippus grows faster and attains significantly greater size when fed as a larva on several species of Asclepiadaceae (milkweeds) containing cardiac glycosides than on one which does not.Acknowledgment. I thank Professor D. Schneider and Dr M. Boppré for sending me a sample of butterflies of Kenya stock reared in the Federal Republic of Germany.     

Arousal threshold in the cat as a function of sleep phase and stimulus significance

Résumé Chez le Chat éveillé après conditionnement au moyen de clicks et de lait, les clicks déclenchent le réveil de manière plus efficace qu'en l'absence de conditionnement. Le seuil d'éveil s'est avéré plus bas lors d'un sommeil accompagné d'ondes lentes de haut voltage que pendant le sommeil paradoxal.

---

---

Supported by NSF Grant No. GB 1965.     

New inversion of the pair no. 3 chromosome in a black rat

Summary A Japanese black rat (Rattus rattus tanezumi) with a subtelocentric pair no. 3 chromosome was found in Gotenba, Japan. By comparison of the length in both members of the chromosome pair, and from the G-ban pattern, the subtelocentrics seemed to have developed from the original acrocentrics by the pericentric inversion.The author wishes to express his sincere thanks to Dr. K. Moriwaki for the help of the collection of the material and also for the skilful technical help of Miss Y. Ochiai. Supported by a grant-in-aid from the Ministry of Education, Science and Culture of Japan (Nos 111510 and 111506). Contribution No. 1125 from the National Institute of Genetics, Japan.     

The stimulus transmitting apparatus in the trichobothria of the bugsPyrrhocoris apterus L. andDysdercus intermedius (Dist.) and its influence on the dynamic of excitation in these sensilla

Correlations exist between ultrastructural characteristics in the stimulus-transmitting apparatus of the trichobothria on the 4th abdominal segment of the bugPyrrhocoris apterus (L.) and the functional characteristics of these sensilla.