Effect of heat stress on conception in a dairy-herd model in the Natal highlands of South Africa.

Regression models are proposed for predicting conception rate in a dairy herd under South African and especially Natal conditions. Conception rate (CR%) was related to mean monthly temperature-humidity index (THI) by curvilinear regression equation model; CR% = 812.7 +/- 28.61 THI - 0.2322THI2 (P = 0.061), and by linear regression equation model; CR% = 188.0 - 1.906THI (P = 0.023). Conception rate was related to numerical month of the year (M) by: CR% = 44.34 + 6.168M - 0.428M2 (P = 0.106). Further investigations to test the proposed regression models under various dairy-herd conditions and to improve reproduction in South African dairy herds are needed.

The shifting of the aortic origin of the brachial arteries in the metamorphosing eel Anguilla anguilla (L.), with remarks on the shifting mechanisms in arterial junctions in general.

In silver eels the arteries supplying the pectoral girdles and fins, arise from a common trunk which branches off from the dorsal aspect of the dorsal aorta, while the origin of this trunk is found at the ventral aspect of the aorta in the leptocephalus larva. The rearrangement of the origin of this trunk is mainly accomplished during metamorphosis, and is related to the rearrangement of the junction of the epibranchial arteries and the aorta. The processes of remodelling the wall of the vessels involved in these rearrangements are discussed against the background of data on similar remodelling, accompanying the rearrangement of arterial junctions during the development of higher vertebrates.

Growth of striated muscle fibres in the M. lateralis of the European eel Anguilla anguilla (L.) (Pisces, Teleostei).

Diameters of red and white muscle fibres were measured in the M. lateralis of eels cultured under laboratory circumstances over a period of 2 years, starting from the glass eel stage. The red fibres of eels less than 10 cm are unique in that their growth involves increase in diameter only. Growth of the red fibres in eels greater than 10 cm, and of the white fibres in eels at all lengths considered, is characterized by an increase in number as well as diameter, the relative importance of these two methods of growth being related to factors other than the length of the animal. Satellite cells may play an important part in the addition of new, small muscle fibres.

Morphological and functional aspects of the arrangement of connective tissue and muscle fibres in the tail of the Mexican axolotl, Siredon mexicanum (Shaw) (Amphibia, Urodela).

In the lateral musculature of the axolotl tail a multipennate arrangement of muscle fibres is found in the 3rd postanal myomere and all following myomeres. This arrangement appears in larval stages as soon as the myomeres concerned are fully differentiated. Within a myomere a uniform degree of contraction of the muscle fibres may be achieved either by helical arrangement as seen in Teleosts, by diminishing fibre length in medial direction or by a combination of both phenomena. The relation between muscle fibre length and angle of insertion in the myomeres showing pennate arrangement is approximated by the Benninghoff and Roll-häuser equation but the values recorded deviated systematically from the values calculated. In the rather slender tail of the axolotl the transition from the helical or parallel fibre system into the pennate arrangement will be in favour of the development of relatively strong bending moments in the region concerned while a reasonable uniformity of the rate of contraction is maintained.