On the parafollicular cells in the thyroid gland of the bovine foetus

The thyroids of 117 bovine foetuses were studied by some histochemical and selective staining methods with respect to the occurrence of parafollicular cells. Furthermore, 7 foetuses were studied by electron microscopy. The length of the foetuses varied from 6 to 72 cm corresponding to an estimated age of about 2 to 9 months. Parafollicular cells were observed in the thyroids of all foetuses examined. The ultrastructure of the parafollicular cells in the foetuses differed very little from that described in adult animals. Histochemically, Luxol fast blue positive phospholipids and α-glycerophosphate dehydrogenase activity could be observed in the cells. The Solcia-Sampietro method gave positive results in most of the foetuses examined. The reactions observed at light microscopic level were rather faint in the youngest foetuses. The functional aspects of the results are discussed.