(1) By contrast, the growth of the oocyte in relation to the follicle in monotremes in linear throughout the whole period of follicular growth.
(2) The mammals examined included 3 eutherian, 2 marsupial and a monotreme species and the reptiles 2 saurian, 1 crocodilian and 1 testudine species.
(3) Monotreme enamel has been interpreted as representing a structural stage intermediate between that of known multituberculates and extant tribosphenid mammals.
(4) No sex difference was observed in any monotreme tissue.
(5) The possible role these and the native rodents, marsupials and monotremes would play should an exotic disease of livestock enter Australia is discussed.
(6) A dorsal pterygoid element and a ventral ectopterygoid element can be recognised during the development of monotremes, marsupials and eutherian mammals.
(7) The ratio of the contents of the two major mammalian ganglioside fractions GD1a and GT1b is generally in the range of 1.0 and even higher; in the heterothermic platypus from the monotremes and in hibernators among the placental mammals, however, it is much lower (about 0.8).
(8) Because monotremes and marsupials diverged independently from eutherian mammals, this finding implies that the whole human X short arm region is a relatively recent addition to the X chromosome in eutherian mammals.
(9) Several lines of evidence suggest that electroreception has evolved independently in this monotreme.
(10) Since marsupials and monotremes diverged independently from eutherians, these data suggest that HSA 21 genes were originally located in two separate autosomal blocks.
(11) Here we establish that the platypus, the Australian nocturnal diving monotreme, can locate and avoid objects on the basis of d.c. fields.
(12) In monotremes the elements remain distinct and show specialised features, including a hamular cartilage in the ectopterygoid of one specimen of Ornithorhynchus.
(13) In order to extend comparative mapping studies to the monotreme mammals (subclass Prototheria), somatic-cell hybrids were obtained between Chinese-hamster cells deficient in hypoxanthine phosphoribosyltransferase (HPRT) and platypus fibroblasts.
(14) The amino acid sequence showed approximately 85 differences from mammalian, monotreme and bird myoglobins.
(15) There was no ligament of the femoral head in the hip joints of the monotremes, and it is suggested the absence of a ligament may be significant in the development of the cavity.
(16) The present study examines the cartilaginous epiphyses and physes from the knee and hip of the rat and the two Australian monotremes (platypus, Ornithorhynchus anatinus and echidna, Tachyglossus aculeatus).
(17) A region represented by the short arm of the human X is common to the X in all eutherians, but is autosomal in marsupials and monotremes; thus it was not a part of the original X, and must have been acquired by the X early in the eutherian radiation.
(18) The enamel of the fossil monotreme is prismatic and tubular and displays large areas of Pattern 2 prism packing.
(19) This estimate agrees well with similar estimates made using alpha- and beta-globin sequences, in contrast to widely differing estimates of dates of divergence for monotremes using the same three globin chains.
(20) Xenoantisera directed against human heavy chain isotypes allowed the serological identification of IgM and IgG immunoglobulins in the echidna (Tachyglossus aculeatus), a monotreme which is one of the most primitive species of extant mammals.