Helen D. Park

The relation of oxygen consumption to ambient oxygen concentration during metamorphosis of the blowfly, Phormia regina

Abstract At 1–5 days of pupal life in Phormia regina at 25°C, respiration becomes oxygen-limited at ambient oxygen concentrations between 15 and 10 per cent. In 1 per cent O 2 it is reduced to about one-fifth of the corresponding control levels. One and 5 day pupae tend to be somewhat more sensitive to hypoxia than other ages. Pupae exposed to pure nitrogen for 4 hr show a subsequent respiratory overshoot in air as compared with controls. Considering the overshoot as repayment of oxygen debt, the theoretical extent of repayment in 7 hr is 14 or 26+ per cent, depending on whether development is considered to stop or to continue during anoxia. The corresponding repayments in pure oxygen are 26 and 33+ per cent, suggesting that the rate of postanoxic respiration in air is physically limited.

Osmium tetroxide-zinc iodide staining of Golgi elements and surface coats of hydras.

Hydras treated for 4 hours with osmium tetroxide-zinc iodide (OZI) exhibit complete impregnation of Golgi saccules and vesicles, staining of the fibrillar surface coat of the gastrodermis, and staining of the inner surface of certain clear, intracellular vacuoles. No deposition occurs within the epidermal surface coat, the intercellular spaces, or the mesoglea. When the OZI solution is adjusted to pH 7.0, Golgi structures stain, but deposition along surface coats is no longer noted. Increased or decreased duration of treatment with OZI produces incomplete Golgi permeation and variable loss of surface coat staining. Hyaluronidase pretreatment of living hydras prevents OZI deposition along the gastrodermal luminal surface and within Golgi zones, suggesting that OZI could be staining mucosaccharides in these sites.

Reproduction in Paramecium as Affected by Small Doses of X-Ray and Beta Radiation

Summary Beta radiation administered at a level of from 0.77 to 3.13 rep per hour and X-ray radiation given at 4 or 8 r per hour stimulates reproduction in Paramecium. The stimulation is not due to mutation since it disappears immediately on removal of the cell from the influence of the radiation.

CARBON DIOXIDE TENSION AND SEXUAL DIFFERENTIATION IN HYDRA

1. One hundred-and 10-hydra cultures of Hydra littoralis and 10-hydra cultures of H. pseudoligactis and H. (sp.) were maintained 14-50 days in culture solutions equilibrated with gas mixtures varying in CO2 content from 0.0% to 5.6%.2. Two culture solutions and three methods of gassing cultures were used.3. The results were:a. Asexual H. littoralis began to differentiate sexually within 1-4days under all experimental conditions; initial sexual differentiation was temporary and was often followed by a second period of gonad development. In several experiments, percentages of sexual hydras tended to rise and fall together, regardless of treatment.b. H. littoralis cultures containing 46-72% sexual animals bubbled 22 hours daily with room air or 5% CO2 in air were 95-100% asexual by day 12. Continued bubbling for the next 4 weeks with 5% CO2 in air was as effective as bubbling with room air in maintaining asexuality.c. No sexual differentiation occurred in H. pseudoligactis or H. (sp.) cultures exposed 18 day...