The Royal Society discussed Letter L-128 of 1683-07-16 about the male seed in egg yolks
The Royal Society wanted Leeuwenhoek to examine the eggs of silkworms and it requested again on 17/27 June 1685, but Leeuwenhoek's next letter on silkworms is Letter L-189 of 1687-07-11.
Birch, History, vol. IV, p. 217, 25 July 1683 (O.S.) in London:
It was observed upon Mr. LEEWENHOECK's letter of July 16th, that the point, where the animal of the male seed is to be first received, and where it is to be first nourished, is placed in the yolk of the egg; and accordingly, that Mr. LEEWENHOECK made search for the animal in the yolk of the egg: whereas he ought to have looked for it in the white; which is certainly the first nourishment of the chicken, the colliquamentum being there to be found after twelve hours incubation.
It remained to know, whether Mr. LEEWENHOECK by the abovementioned point did not mean the cicatricula, which adheres to the yolk of the egg.
Mr. LEEWENHOECK having hitherto been unsuccessful in tracing the animal, it was desired, that he would examine a greater variety of eggs, and particularly those of a silk-worm.
