MISCELLANEOUS OBSERVATIONS ONHYDRA, WITH SPECIAL REFERENCE TO REPRODUCTION

Abstract

1. Directions for the cultivation of hydra are given. 2. The phenomenon of depression, in which there is a shortening and gradual loss of tentacles and column from the distal end proximally, is of common occurrence in hydras and probably represents a lowered metabolic state. It is induced by rich feeding, high temperature, sensescence, fouling of the culture water, lack of oxygen, transfer to clean fresh water. Recovery may be spontaneous or may by induced. 3. Irregular adventitious budding tends to occur in senescent, extremely elongated, depressed, and sexual specimens, that is, specimens in a low metabolic state. Under such conditions buds may be retained on the parent far beyond the normal time, giving rise to so-called colonies. 4. Abnormalities, such as forked tentacles and forked distal and basal ends arise chiefly in recovery after depression. Forked distal structures may also arise by retention of a bud. 5. Longitudinal and transverse fission are probably not normal modes of reproduction of hydra but are methods of regulation of previously existing abnormalities or occur in specimens in a low metabolic state. 6. Tests by the susceptibility method have shown that: (a) Starvation beyond four days increases the metabolic rate. (b) Depressed animals have a lower metabolic rate than controls starved the same length of time. (c) Animals recovered from depression have an equal or higher metabolic rate than controls starved the same length of time. (d) The metabolic rate of sexually mature animals is lower than that of asexual controls and that of females is lower than that of males. 7. The formation of sex organs can be induced in Pelmatohydra oligactis in about three weeks by lowering the temperature about ten degrees. 8. In diœcious species of hydra, the sex of asexually produced offspring is the same as that of the parent. 9. Hydras may become sexually mature in the laboratory without any apparent cause. Such sexual animals and their asexual offspring tend to remain and to become sexual. 10. Sexual specimens when fed bud while still retaining the gonads. 11. Sexual specimens when fed may lose their gonads for short periods but tend to develop them again as do alse their asexually produced offspring. 12. Females when fed remain of normal size and bud normally. 13. Males when fed tend to elongate greatly and thereupon produce buds irregularly and adventitiously over a considerable length of column. 14. The buds of such male specimens tend to be retained indefinitely forming complex colony-like specimens. 15. Such retained buds commonly develop a foot in situ with which they may be fastened to the substratum. 16. Colonies formed in this manner split up eventually by one or more transverse constrictions which pass just proximal to the budding zone of the main component if any or between the bases of the components when they are equal. 17. Male specimens when fed may not bud but instead may give rise to accessory feet at one or more points along the column; such tend to divide by transverse fission just proximal to one of the feet. The proximal piece formed by such a fission regenerates a foot, not a hydranth, at its distal end; it then buds near its middle and the bud if fed grows up at right angles to the axis of the piece using the two or more feet as base. 19. Reversals of polarity due to the control of parts of the parent column by buds were frequently observed. 20. All of the facts indicate that each peristome controls a certain length of column and prevents the formation of a bud within the limits of that control. The control is diminished in senescent, depressed, and sexual specimens. Each foot also controls a short length of column and prevents the formation of a bud within that distance.