Exposure of male hamsters to cycles of 1 hour of light and 23 hours of darkness causes atrophy of the gonads. Pinealectomy prevents this atrophy, but has no effect on animals exposed to light-dark cycles of 16 : 8. Likewise, removal of both eyes induces gonad atrophy which is prevented by pinealectomy. These data emphasize the importance of the pineal gland in the regulation of photoperiodic influences on the gonads.

Removal of the pineal organ from small rodents may be rapidly accomplished by ( 1 ) immobilizing the skull in a head mounting device and (2) by cutting and removing a circular disc of bone overlying the pineal area with the use of a dental machine and a specially designed circle cutter. Recent investigations in this laboratoryhave required the use of large numbers of pinealectomized hamsters. Initially, the operation performed with a hand trephine or a dental machine using a n ordinary burr drill was fraught with technical difficulties, excessive bleeding and relatively high mortality. The following procedure using a standard dental machine was developed which permits rapid pinealectomy, minimal bleeding and nearly 100% survival.The hamster skull is small and the skin is so loose that the necessary immobilization of the head to permit drilling is almost impossible. This difficulty was solved by building a base of lucite fitted with ear bars and a n adjustable tooth bar. Essentially this head holder is simply a modification of any standard stereotaxic instrument base.A disc drill was made from stainless steel stock turned down and drilled so as to form a thin walled tube as shown in figure 1. Coarse teeth were filed at one end of a short piece which was attached to the shaft of an ordinary dental drill either by silver solder or by boring and tapping holes in the sides to accommodate 0-80 stainless steel Allen screws. A collar was fitted around the drill, adjusted to the desired depth of cut and tightened with Allen screws. Although figure 1 shows serrations with positive rake when rotating in a clockwise direction, further study has shown that teeth with negative rake are as good or better; the latter appears to produce less hemorrhage from the diploic vessels.The animals are anesthetized, the bases of the ears are slit vertically to expose the ear canals (not mandatory) and the head of the animal is rigidly mounted i n the ANAT REC., 153: 19-22.holder ( fig. 2). The scalp is cut anteroposteriorly along the midline from between the eyes to beyond the base of the skull. The skin flaps are reflected and the underlying fasciae and the insertions of the temporal and occipital muscle masses are scraped free in a n area wider than the diameter of the collar. Careful removal of these tissues from the field is necessary to prevent entanglement with the drill and collar during the subsequent step. At this

Harderian glands of female or castrated male hamsters contained scattered luminal pigment deposits and a single cell type. TWO cell types were found in the glands from intact males. Glands from both male and female animals showed abundant cytoplasmic lipids. Pigment formation appeared to be endogenous and in some cases occurred by extrusion of cells from alveolar walls and their subsequent transformation. Holocrine secretion was demonstrable. Porphyrin concentrations in the glands from females were increased three weeks after bilateral blinding and decreased following hypophysectomy, ablation of one Harderian gland, unilateral blinding, treatment with thiourea or exposure to an environmental temperature of 8°C. Ovariectomy or ovariectomy plus treatment with 17-a-estradiol for three weeks had no effect on the Harderian glands nor did pinealectomy. Porphyrin concentrations in the glands from male hamsters were extremely low. Castration increased these concentrations over 100-fold and modified the morphology toward that of the female while testosterone proprionate treatment prevented these changes. Administration of H3-thymidine and subsequent radioautography revealed a peak in mitotic activity between 9: 30 PM and 12: 30 AM at the end of the light period or the beginning of the dark period. Longterm blinded or blinded, castrated males had Harderian glands which were microscopically "lacelike" due to intense steatogenesis.

Global Positioning System (GPS) telemetry is used extensively to study animal distribution and resource selection patterns but is susceptible to biases resulting from data omission and spatial inaccuracies. These data errors may cause misinterpretation of wildlife habitat selection or spatial use patterns. We used both stationary test collars and collared free‐ranging American black bears (Ursus americanus) to quantify systemic data loss and location error of GPS telemetry in mountainous, old‐growth temperate forests of Olympic National Park, Washington, USA. We developed predictive models of environmental factors that influence the probability of obtaining GPS locations and evaluated the ability of weighting factors derived from these models to mitigate data omission biases from collared bears. We also examined the effects of microhabitat on collar fix success rate and examined collar accuracy as related to elevation changes between successive fixes. The probability of collars successfully obtaining location fixes was positively associated with elevation and unobstructed satellite view and was negatively affected by the interaction of overstory canopy and satellite view. Test collars were 33% more successful at acquiring fixes than those on bears. Fix success rates of collared bears varied seasonally and diurnally. Application of weighting factors to individual collared bear fixes recouped only 6% of lost data and failed to reduce seasonal or diurnal variation in fix success, suggesting that variables not included in our model contributed to data loss. Test collars placed to mimic bear bedding sites received 16% fewer fixes than randomly placed collars, indicating that microhabitat selection may contribute to data loss for wildlife equipped with GPS collars. Horizontal collar errors of >800 m occurred when elevation changes between successive fixes were >400 m. We conclude that significant limitations remain in accounting for data loss and error inherent in using GPS telemetry in coniferous forest ecosystems and that, at present, resource selection patterns of large mammals derived from GPS telemetry should be interpreted cautiously.

Throughout a 24-h period, immunoreactive melatonin concentrations in Harderian glands of female golden hamsters were approximately 200 pg/mg protein with a significant decline to 80 pg/mg protein only at about 0600, 2 h after light on. Concentrations in glands of males are diurnally constant and low (ca. 20 pg/mg protein). Castration increases immunoreactive melatonin in glands of males to female levels. While blinding alone had no effect, it did prevent the castration-induced increase. Lower concentrations were measured in glands of blinded or blinded ovariectomized females but this decrease was not significant. These data suggest that immunoreactive melatonin concentrations in the Harderian glands of hamsters are controlled by testosterone or its derivatives; these same factors also control the male or female character of these glands.