TEMPERATURE AND FREQUENCY OF CARDIAC CONTRACTIONS IN EMBRYOS OF LIMULUS

Temperature characteristics for frequency of myogenic heart beat in Limulus embryos, before the onset of nervous control of the heart, were found to be 11,500; 16,400; 20,000; 25,500. The two first values are the best established. The different values pertain to the hearts of different individuals outwardly similar, and to the hearts of single embryos in different parts of the temperature range. These values differ from that known in connection with the control of the heart beat through the cardiac ganglion. The occurrence of critical temperatures, also, is not the same in all embryos. These facts are employed in a discussion of temperature relations in pulsating explants of chick myocardium.     

ON THE CONTROL OF THE RESPONSE TO SHADING IN THE BRANCHI? OF CHROMODORIS

The branchial plumes of Chromodoris respond, by contraction, to a decrease in light intensity. This response is obliterated by high temperatures (above 32°) and by direct sunlight, and is possible only within a limited range of alkalinity of the sea water. A concealing retraction of the whole gill-crown is reflexly determined by the self-contraction of the individual plumes under "optimal" conditions of light, temperature, and alkalinity. This protective response of the branchiæ is superimposed upon their simple system of fundamental activities (protrusion, retraction) apparently concerned with regulating the respiratory exchange of the nudibranch.     

THERMAL INCREMENTS FOR PULSATION-FREQUENCY IN "ACCESSORY HEARTS" OF NOTONECTA

The frequencies of pulsation of the "accessory hearts" in the isolated swimming-legs of Notonecta were studied in relation to temperature, with the idea that in such organs central nervous control is impossible, and that in an isolated system irreversibly proceeding toward death it might be expected that further evidence would be found regarding the supposed specific significance of critical thermal increments. A number of values of µ are found, commonly 8,200; 16,200; or 32,200; less frequently 11,400; 19,800; and 24,500. These values are definitely contrasted with that (12,300) typical for heart beat frequencies in arthropods. They exhibit interrelationships of the sorts already found in other cases. There occur also sharp irreversible changes in frequency of pulsation, which may or may not be accompanied by change of increment. The net result is held to be confirmatory of the interpretation of thermal relations proposed in earlier papers.     

GALVANOTROPISM AND "REVERSAL OF INHIBITION" BY STRYCHNINE

The cathodically galvanotropic orientation of nemerteans, Lineus, and the anodic orientation of the gephyrean Echiurus, are reversed by the action of strychnine under conditions such that the typical "reversal of inhibition" induced by this substance is apparent. Nicotine does not give this result. Since it is necessary to assume that the strychnine effect is due to action upon the central ganglia, and since the galvanotropic effect depends upon action of the current on nerve cell bodies of the central ganglia, it must be assumed that the locus of reversal by strychnine is not perikaryal, but presumably synaptic.     

ON CRITICAL FREQUENCY AND CRITICAL ILLUMINATION FOR RESPONSE TO FLICKERED LIGHT

The curve of mean critical flicker frequency as a function of illumination has been determined for the reaction of the sunfish Lepomis to flicker. It exhibits expected quantitative disagreements with the curve of mean critical illumination as a function of flicker frequency in the same organism. The form of the dependence of the variation of critical frequency of flicker upon illumination can be predicted from a knowledge of the way in which variation of critical illumination depends upon flicker frequency. It is pointed out that these findings have an important bearing upon the interpretation of the data of intensity discrimination.     

EVIDENCE FOR SEVERAL SIBLING BIOLOGICAL SPECIES CENTRED ON MYRMECIA PILOSULA (F. SMITH) (HYMENOPTERA: FORMICIDAE)

Abstract
Chromosome numbers of 2n = 2,9,10,18,19,20,21,22,23,24,25,26,27,30,31 and 32 were found for Myrmecia pilosula (F. Smith). Karyotopic and morphological evidence indicates the presence of a " M. pilosula " complex with at least 3 biological species.     

THEORY AND MEASUREMENT OF VISUAL MECHANISMS : VII. THE FLICKER RESPONSE FUNCTION OUTSIDE THE FOVEA

The several parameters of the flicker response contour (F – log I) are considered as a function of wave-length composition (white, blue, and red) and light-time fraction, for an extra-foveal region (monocular, temporal retina). These data are compared with those secured for the same image area centrally fixated at the fovea. The systematic changes in the parameters are shown to be in rational relation to other relevant excitability data. Since for two retinal regions the primary contours are quite different, the systematic nature of the behavior of the parameters in the two cases is a real test of the power of the analysis proposed. Theoretical interpretation is required to deal with the properties of sets of performance contours under systematically varied conditions, and cannot rely simply on the comparison of (for example) two contours under the same arbitrary conditions at two retinal locations. In particular it is emphasized that a qualitative separation must be made of the two factors of (a) number of units and (b) the frequencies of their actions, before the wave-length problem can be dealt with effectively.