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Hibernating mammals drastically lower their rate of oxygen consumption and body temperature (Tb) for several weeks, but regularly rewarm and stay euthermic for brief periods (, Summary: In hibernating garden dormice, torpor bout length depends on oxygen consumption. This indicates that torpor duration is determined by accumulation of a metabolic imbalance, which is cleared during periodic rewarming.

[Graphic][1] The incubation of eggs is a critical stage in the life of a bird. Although the eggs need the warmth of their parent's body to develop, most birds need to leave their eggs for brief periods to forage for food. When the adults are gone, the egg's temperature will fall and might

[Figure][1] Hibernation is a fascinating, yet enigmatic, physiological phenomenon utilized by some mammals to successfully cope with the extreme conditions of a harsh season such as winter. During the inhospitable season, hibernating animals repeatedly alternate between brief periods at

The swimming speeds attained by hatchery-reared plaice larvae have been determined by measurements made (a) in still water, and (b) against a current flowing through a long glass tube. In still water contact stimuli were used to initiate swimming. No optomotor response was found, and it was not possible to use the ‘fish-wheel’ of Bainbridge (1958). Larvae in the experimental tube stemmed the current for brief periods only, their position then being near the periphery of the upper quadrant. The speeds were found to show a linear relationship to larval length multiplied by the height of the post-anal musculature. Observations in still water show that these values correspond to those of steady swimming: they are not maximum speeds. Speeds ranged from about 1·5 cm./sec. when newly hatched to 9 cm./sec. in late larvae. Darting velocities of up to 15 cm./sec. were recorded with half-grown (stage III) larvae. In such larvae cruising speeds were about three fish-lengths (3L) per second, and the maxima about 10L/sec. The design of gear for collecting fish larvae at sea is discussed. Only a high-speed tow-net, towed at about ten times the velocity attainable by the largest larvae and giving almost no warning of its approach, can be considered to collect a quantitatively balanced sample.

Since 1955 Harker’s work on the control of cockroach activity rhythms by a hormonal clock in the sub-oesophageal ganglion has stood largely unchallenged, but recently Roberts (1966) has questioned several of her claims; in particular he finds it impossible to transfer rhythms by implanting this ganglion. Sub-oesophageal ganglia from rhythmic donors were implanted into 29 headless Periplaneta americana in a variety of ways and three different actographs used. In 2 cases the hosts showed bursts of activity for 2 or 3 days after implantation, roughly coincident with the donor’s previous rhythm; a further 8 implanted animals showed rather uncertain signs of an induced rhythm, but the remaining 19 were all apparently arrhythmic. Cauterization of the neurosecretory cells of the sub-oesophageal ganglion in situ showed that cockroaches can remain rhythmic in the absence of the cells described by Harker (1960 c), and probably in the absence of all cells in this ganglion which are stained by paraldehyde-fuchsin. Implantation of abdominal ganglia plus their respective neurohaemal organs (Brady & Maddrell, 1967) did not elicit rhythms in eight headless hosts. Cutting the circum-oesophageal commissures, or post-sub-oesophageal ganglion connectives, like beheading, appears to interfere seriously with the rhythmic expression of activity; one animal remained apparently rhythmic after this operation, however. Harker’s proposal for a second clock (1960b) requires that phase-shifts of less than 5 hr. shall be completed within a single activity cycle; this did not occur in the twelve cases observed, phase-shifting being gradual and taking several days before reaching the entrained steady-state. It is suggested that most of the divergent results of Harker, Roberts and Brady could be plausibly correlated if cockroaches have an electrical pace-maker in the brain co-ordinating rather ephemeral neuro-endocrine rhythms in the nerve-cord ganglia.