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AGGREGATION in planktonic organisms is often observed, both in the sea and in fresh water, and several explanations have been put forward to account for it. Uneven light intensity can often lead to aggregation; but other reasons must be put forward to account for swarms under uniform illumination. Some authors consider the animal's own behaviour to be responsible for swarming; thus social behaviour has been invoked in Cladocera1, chemosensitivity in Hemimysis2 and visual orientation to explain Mysid shoaling3. Other authors regard physical processes as being largely or entirely responsible, such as wind-generated turbulence4, retention in convection cells5 or in a weak convergence, aided by photopositive swimming6.

Bracken et. al. (1962) showed that under natural conditions tabanids are attracted to decoy silhouettes painted with certain pigments. The paint pigments used in the field orientation study reflected a mixture of wavelengths to varying degrees. Preliminary tests were therefore carried out in the laboratory where filters transmitting narrow bands of the spectrum were used. Although tabanids in general are not active in the dark a study of their orientation to light under skotoptic conditions may help to understand their behaviour in the field since the horse fly apparently depends largely on visual orientation to locate its hosts. The present study was conducted with this end in view and as a basis for future studies of the chemistry of vision.

AT least some, and perhaps most, pinnipeds of the families Phocidae and Otariidae are nocturnal feeders1. The eyes of these predators, being sensitive to very low light intensities2, are suited for use at night and in deep water. During the day the visual acuity of the California sea lion (Zalophus californianus) allows this animal to discriminate a size difference ratio as small as 1.06 : 1 (ref. 3). A great deal of vocalizing occurs among pinnipeds, both above and below the surface of the water1,4–6. This fact, along with experimental work such as that of Mohl with the harbour seal (Phoca vitulina)7, indicates that hearing is generally well developed. Poulter suggested that the California sea lion, and probably other species, is able to capture prey in darkness by utilizing an echo-ranging sense similar to that known to occur among cetaceans4. However, subsequent work5,6 has failed to support Poulter's theory. Nevertheless, as “individuals totally blind but in a good state of health have been reported”1, the possibility that such a sense may bo developed when needed should not be dismissed lightly.

Visual orientation judgments were made during right head tilt, left body tilt, and left trunk tilt, each of 30 deg. In these postures the otolith, neck, and trunk systems are stimulated in pairs. The hypothesis that the visual vertical during trunk tilt is equal to the algebraic sum ofthose in the same direction ofbody tilt and the opposite head tilt was tested and accepted. This result demonstrates the interaction of these postural systems in visual orientation, and complements the confirmation of the same hypothesis for the visual aftereffect following prolonged tilt.

The Daphnia eye is suspended in position not by ligaments but by a membrane coming radially, in the coronal plane, from a great circle around the eye. to form a water-tight seal between eye, and carapace. Because the chamber thus separated from the haemocoel must remain constant in volume, haemocoel pressure combines with muscle tensions and resulting tensions in the membrane, to produce eye rotations but very little translationary movement—as in a universal joint. This system permits relatively little cyclotorsion, however. The implication of such restriction for current theories of cladoceran visual orientation is noted.

The shape of the primary auditory filter has been calculated from masking measurements [R.D. Patterson, J. Acoust. Soc. Am. 56, S36 (1974)], It may also be determined using subthreshold summation, as Kulikowski and Kingsmith [Vision Research, 13, 1455–1478 (1973)] have done for visual feature detectors. The masked signal is a combination of 500 Hz with another frequency (e.g., 515 Hz) of equal or lower intensity. The threshold intensity of 500 Hz is plotted in linear coordinates as a function of the intensity of the other component, and the resulting curve determines two points on the filter characteristic. The relative gain of the 500‐Hz filter at 515 Hz is given by the negative slope of the function at low intensities of 515 Hz, and that of the 507.5‐Hz filter at 500 or 515 Hz is independently determined from the threshold when the two components are equal. Preliminary results using a noise level of 0 dB/Hz suggest a Gaussian filter of about 25‐Hz bandwidth, whereas masking measurements suggest about 65 Hz. For visual orientation detectors, Kulikowski et al. [Visual Research, 13, 1479–1486 (1973)] found bandwidths a factor of 4 narrower when using subthreshold summation than those found by masking.

Recent advances in neonatology have enabled an increasing number of small premature infants to survive. While research on the physiological aspects of prematurity has been abundant, little is known about the early developmental course of these infants. This study examines the development of visual orientation in premature infants and has important theoretical and clinical implications. All infants were assessed using visual items from the Brazelton Scale. In the first 3 groups were 36 AGA, premature infants, breathing room air by 32 weeks gestation. Group 1 was assessed at weekly intervals from 32 to 37 weeks and at 40 weeks. Groups 2 and 3 served as controls for repeated testing. In Group 4 were 12 full-term infants tested at 2 days. Visual orientation increased steadily from 32 to 40 weeks. At 40 weeks, Group 1 was no different in visual behavior from Group 4. However, infants tested less frequently (Groups 2 and 3) performed less well than Groups 1 or 4. Theoretically these results support that view that visual development is gradual but can be affected by experience. Clinically, intervention strategies to enhance visual orientation are recommended in light of previous studies demonstrating the effects of visual behavior on mother-infant interaction.

Data from the NINDS Collaborative Study and others suggests that infants of diabetic mothers do more poorly than matched controls in specific development tests at age 4 years. This study assesses the behavior of these newborns of diabetic mothers (NDM's) in order to understand the genesis of these later problems and to design appropriate interventions. Ten full-term NDM's delivered by elective Caesarian section were compared to ten healthy full-term newborns delivered by elective Caesarian section on the Brazelton Neonatal Behavioral Assessment scale administered on days 3 and 5. All NDM's were free of all anomalies, metabolic and respiratory problems and considered healthy by their pediatricians by day 3. Brazelton scale data were analyzed with an a priori established cluster and profile scheme. The NDM's did significantly more poorly than the control newborns in physiological responses to stress and on interactive processes (Repeated measures ANOVA, p≥0.05, p≥0.001). In particular, the NDM's were more tremulous, had more startles and showed more color changes with handling even though they were normoglycemic and normocalcemic. Furthermore, NDM's behaved differently than controls on those behaviors considered important elicitors of caregiving by parents: attractiveness, need for and use of stimulation, visual orientation, sustaining periods of alertness and molding to the examiner's body during cuddling. It is speculated that the behavioral difficulties demonstrated in these newborns may influence early interaction with caregivers, make bonding more difficult and set the stage for later problems.

These ten papers, republished in homage to Sir Gordon Holmes on the occasion of his eightieth birthday, deal with three subjects with which his life and work have been particularly identified—the cerebellum, the cortical representation of vision, and visual orientation and attention. The papers concerning the cerebellum include the early paper on its connections with the inferior olives, that describing the form of cerebellar degeneration now known as the Holmes' type, the study of the symptomatology of cerebellar tumors, and the classic Croonian lectures of 1922 on the clinical symptoms of cerebellar disease and their interpretation, ending with the discussion of the functions of the cerebellum taken from the Hughlings Jackson lecture of 1939. Many of these papers have not been readily available, and, if for no other reason, the guarantors of Brain have provided a real service in making them again obtainable by students of neurology; but this collection