Volume 31, Issue 5
May 1950, pages 235-286
pp 235-251 May 1950
The yolk-sac which is disposed towards the mesometrial side establishes placental relationship with the uterus. The yolk-sac placenta is at first non-vascular and later becomes vascular.
As development proceeds the extension of the exocœlom and the expansion of the amniotic cavity results not only in the obliteration of the yolk-sac placenta, but, in the invagination of the yolk-sac roof over the distal bilaminar omphalopleure.
The allantois is disposed towards the antimesometrial side. The allantois gradually spreads towards the lateral sides below the placenta and progressively replaces the yolk-sac placenta.
The changes involved in the formation of the definitive labyrinthine placenta are : (i) The penetration of the syncytiotrophoblast by the tropho-blastic chords, (ii) the invasion of the cavities thus formed by the allantoic mesenchyme and fœtal vessels, (iii) the loss of the cell boundaries in the cytotrophoblastic cords, which therefore occurs as a network of cytoplasm with flattened nuclei embedded in rows.
The final placenta is therefore of the labyrinthine hasmochorial type.
pp 252-286 May 1950
The studies on the length frequencies, size groups and age groups of the Oil Sardines of Malabar Coast for the period 1936–37 to 1942–43 have been made and the year classes which contributed to the Oil Sardine fishery in the different years are indicated.
The movements of the Oil Sardines and the spawning and survival of the young Oil Sardine on the Malabar Coast seem to indicate a correlation with the surface temperature and specific gravity of sea water and the availability of food. The effect of the surface temperature on the movements of adult sardines month by month and year by year has been indicated.
The variations in the surface temperature in the in-shore regions and off-shore regions and on the coasts are discussed in relation to the appearance of Oil Sardine. It is suggested that further investigations on the age of the Oil Sardine and the occurrence of the fish in the off-shore regions, beyond the present fishing limits, in different months may further aid in appraising the causes for the fluctuations of the Oil Sardine fishery.