The development of phosphomonesterases in the testes of prepuberal chicks.

1. The biochemical development and histochemical localisation of phosphomonoesterases in the testes of prepuberal chicks have been studied. 2. Maximum acid phosphatase activity was observed at 12 weeks with a decrease in enzyme activity after this age, whereas alkaline phosphatase activity fluctuated with age. 3. Acid phosphatase activity in chicks was similar to that of the cockerel in being tartarate-insensitive. 4. There was a low level of significant correlation between acid phosphatase activity and testes weight. 5. Both alkaline and acid phosphatase activities were observed in the basement membrane of the seminiferous tubules, and acid phosphatase activity also in the various spermatogenic elements. 6. The results suggest that acid phosphatase is more involved in spermatogenesis, and more widely distributed than alkaline phosphatase in testicular tissue during testicular development.     

The testosterone level in the testes of silver foxes during prenatal development]

The level of testosterone in serum and testes of the silver fox fetuses on days 31, 35, 40, 45, and 50 of gestation was determined using radioimmunoassay. In testes, testosterone was first detected at day 31; then its level gradually increased. Serum testosterone was detected only at day 40. Subsequent increase in its concentration was insignificant. Human chorionic gonadotropin stimulated testicular testosterone production in vitro beginning from day 40. We suggest that in the silver fox, testes are capable of responding to gonadotropins already by the day 40 of prenatal development but the formation of pituitary-gonadal axis proceeds until the end of embryogenesis.     

Feeding strategies in the development of food recognition in young chicks

Young chicks were observed in a series of 10-min tests in which a dish of food and a dish of sand were simultaneously available. Most chicks learned to ingest primarily food, but all chicks continued to ingest at least some sand. The pattern of ingestion varied widely among individuals. Analysis of the data suggested that the relative increase in food ingestion was due to an appetite for food that developed as a result of an association between the visual and the tactile/gustatory stimuli from the food and the positive long-term after-effects of food ingestion. Sand remained an attractive particle. Further analysis provided evidence for a number of short-term motivational factors: positive feedback from stimuli from the mouth, short-term after-effects of food ingestion, and a mechanism for switching attention. These motivational factors determine a pattern of sampling behaviour that on the one hand ensures that chicks continue to ingest different types of particles, while on the other hand it sets up the conditions necessary for the development of an appetite for particular particles.