Changes in serum concentrations of estradiol‐17β, testosterone, 17α,20βdihydroxy‐4‐pregnen‐3‐one, and vitellogenin were investigated during ovarian development induced by injection of a salmon pituitary extract in cultured European eel Anguilla anguilla. Vitellogenesis was induced with a weekly dose of 50 mg pituitary extract/kg body weight. In eels receiving that dose, gonadsomatic indices ranged from 20–43% after the 10th–11th weekly injection. Body weights were relatively stable during vitellogenesis, but increased dramatically during final maturation. Serum estradiol‐17β levels increased slightly during vitellogenesis and peaked at an average of 6.95 ng/mL at final maturation. The profile of serum vitellogenin followed that of estradiol‐17β which increased markedly from an average of 0.36 to 20.72 mg/mL. Control levels of vitellogenin were undetectable throughout the study. Average serum levels of testosterone increased to a peak of 17.74 ng/mL in the early stage of vitellogenesis, followed by a sharp drop to initial levels (3.86 ng/mL) in the late stage of vitellogenesis, and then increased again to an average of 8.84 ng/mL at the final maturation stage. Serum 17α,20β‐dihydroxy‐4‐pregnen‐3‐one was not detected (<50 pg/mL) throughout the experiment. Profiles of serum estradiol‐17β, testosterone, and vitellogenin observed during ovarian development appear different from those found in salmonids and other teleosts. This study indicates, however, that cultured European eels are a useful model for study of gonadal maturation in the eel.

Abstract— Stentor coeruleus responds to a sudden increase in light intensity with a step‐up photophobic response (avoiding reaction), and to collimated light with negative phototaxis. The peaks of the action spectra for the photophobic response and for the phototaxis are in common, 610 nm. 5. coeruleus showed changes in its steady‐state swimming velocity induced with varying intensities of light (photokinesis). The cells swam fast in light regions but slowly in dark ones (positive photokinesis); the mean velocity of swimming was about 0.6 mm/s at 100 lx but reached about 1.0 mm/s at 50000 lx. The peak of the action spectrum for this photokinesis was about 680 nm. The organism is the first protozoan cell reported to show three types of photoresponse: photophobic response, phototaxis and photokinesis.

Two species of colorless Paramecium, P. caudatum and P. tetraurelia, were suspended in a saline solution. They accumulated in the shaded region when they were introduced into a half-shaded glass tube and illuminated. 520 n m light was most effective in stimulating the accumulation.It used to be generally accepted that colorless species of Paramecium, such as P. caudatum and P. tetraurelia, do not exhibit locomotor responses to ordinary visible light 3'4, though some early workers pointed out that they showed negative responses to very strong light 5'6. We recently examined photoresponses in specimens of P. bursaria, which contain hundreds of symbiotic green algae, Chlorella, and found that they showed locomotor responses to ordinary visible light even after the algae were completely removed from the cells 7. The Chlorella-free, colorless P. bursaria accumulated in the dark region (photodispersal 8) in contrast to the normal, Chlorella-containing specimens which accumulated in the light region (photoaccumulation8). We, therefore, examined the photobehavior exhibited by specimens of colorless Paramecium in a half-shaded glass tube, which was previously employed for demonstrating photoaccumulation in P. bursaria. We found that the 2 species of colorless Paramecium showed photodispersal as Chlorella-free P. bursaria did. Material and methods. Two species of colorless Paramecium (P. caudatum; kyk 201, P. tetraurelia; 51 S VII) were cultured in a wheat-straw infusion at 21 ~ under a fixed illumination cycle (12 h light, 12 h dark). All the experiments were performed on specimens obtained from the cultures 3 h after the light was turned on 9. The specimens were gently washed with a standard saline solution (1 mM KC1, 1 m M CaC12, 1 mM tris-HC1 buffer; pH 7.2) and equilibrated in the solution for more than 20 rain prior to experimentation. In order to examine the photoresponse of Paramecium and its spectral sensitivity, specimens suspended in the saline solution were introduced into a glass tube (4 mm in inner diameter, 40 mm in length) one half of which was covered by a black foil. The tube was placed horizontally under a constant light (4000 lux; white light, 4 x 1 0 ~8 quanta m -2 sec-~; monochromatic light) for 2 rain 7. The number of specimens present in the shaded region of the tube was counted and expressed as a percentage of the total number of specimens in the tube, to indicate the degree of photodispersal. Monochromatic light (half-band width less than 18 nm) was obtained by combined use of interference and cut filters. Thermal radiation Light Dark rt ~~~ R caudatum 9 "~ ~ Rtetraurelia 9 ,

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