. Discovery reports. Discovery (Ship); Scientific expeditions; Ocean; Antarctica; Falkland Islands. 368 DISCOVERY REPORTS pigment so that the colour of the lobes darkens with age. This progressive invasion by blood vessels and phagocytes is shown in Text-figs. 13 A, B, and C, Text-fig. 14 and in Pis. V-VII. In the 'medium' corpora the smaller spiral vessels are more numerous in comparison with the ' young' corpus, and often impart a reddish hue to the pigmented layer so that bodies of this group are usually a darker reddish brown in colour as opposed to the tawny brown, or even yellow colour o
. Discovery reports. Discovery (Ship); Scientific expeditions; Ocean; Antarctica; Falkland Islands. 368 DISCOVERY REPORTS pigment so that the colour of the lobes darkens with age. This progressive invasion by blood vessels and phagocytes is shown in Text-figs. 13 A, B, and C, Text-fig. 14 and in Pis. V-VII. In the 'medium' corpora the smaller spiral vessels are more numerous in comparison with the ' young' corpus, and often impart a reddish hue to the pigmented layer so that bodies of this group are usually a darker reddish brown in colour as opposed to the tawny brown, or even yellow colour of the most recent corpora albicantia. 'Old' corpora Evidence shortly to be presented establishes that this group represents the final stages of regression of whale cor- pora lutea, and within this group there is no further reduction in size. The mean diameter of 2339 ' old' corpora albicantia is 2-013±0-025 cm-> corresponding to a weight of about 5 g., and the size range is from 0-7 to 5-0 cm. They are characterized by increased centripetal penetra- tion of thick-walled blood vessels and closing of the lumen of vessels near the periphery so that the external white connective tissue trabeculae become even more conspicuous. The layer of pigmented tissue is further reduced and concentrated so that it forms a thin hyaline pigmented zone separating the inner, avascular, connective tissue from the outer trabeculae which are now much thicker and composed largely of contorted non-functional thick-walled blood vessels (PI. VII, fig. 1). Text-fig. 13 C shows the macroscopic appearance of one of the least regressed corpora in this group, which still has a conspicuous amount of pigmented hyaline tissue. Text-fig. 13 C, Text-fig. 14 and Pis. V-VII show how the pigmented tissue is replaced by blood vessels growing centripetally. There is no further reduction in the volume of the corpus albicans which is now composed largely of unpigmented collagen, and further regression takes the form o
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