Growth of embryonic avian and mammalian tibiae on a relatively simple chemically defined medium

Synthesis of connective-tissue components. The effect of retinol and hydrocortisone on cultured limb-bone rudiments

1. The action of excess of retinol on chick limb-bone rudiments cultured in chemically defined media has been investigated. 2. After 6 days in vitro, the hexosamine and hydroxyproline contents of the retinol-treated rudiments were much less than those of their paired controls. 3. Synthesis of these compounds, however, was not correspondingly decreased. 4. The control rudiments released hexosamine- and hydroxyproline-containing materials into the culture medium; a greater proportion of the hexosamine and hydroxyproline synthesized was liberated from the retinol-treated than from the control rudiments. 5. Although hydrocortisone in physiological concentrations prevented excessive hydration of the rudiments in culture, it did not significantly inhibit the changes induced by excess of retinol.

Chromosomes of American Marsupials

Studies of the chromosomes of four American marsupials demonstrated that Caluromys derbianus and Marmosa mexicana have a diploid number of 14 chromosomes, and that Philander opossum and Didelphis marsupialis have a diploid number of 22. The karyotypes of C. derbianus and M. mexicana are similar, whereas those of P. opossum and D. marsupialis are dissimilar. If the 14-chromosome karyotype represents a reduction from a primitive number of 22, these observations suggest that the change has occurred independently in the American and Australasian forms.