says, it marks an ‘advance in precision’[150] over other forms as the microspores which fall into the chamber are brought direct to the surface of the underlying megaspore and presumably to the archegonia which, it is reasonable to believe, were disposed in a circle at the base of the annular crevice. Microspores frequently occur in the pollen-chamber and some have been discovered apparently in the act of liberating male gametes[151]. [Illustration: Fig. 408. A, A′, _Lagenospermum Sinclairi._ B, _Lagenostoma_, restoration. C, _Lagenostoma Lomaxi_; _c_, micropyle; _d_, space between integument and nucellus; _e_, cupule; _f_, integument; _ch_, chalaza. D, microspores of _Lagenostoma ovoides._ E, F, _Calymmatotheca Stangeri._ G, H, _Crossotheca Hoeninghausi._ H, section of G in line of arrow. (A, after Arber; B, C, E, F, after Oliver; D, after Benson; G, H, after Kidston.)] [Illustration: Fig. 409. _Lagenostoma._ Transverse section near the micropyle, showing the pollen-chamber, _pc_, the space, _s_, between the nucellus and integument, the fluted canopy with vascular bundles, _v_. (After Oliver.)] The outer wall of the nucellus is bounded externally by a similar circular space (_d_, figs. 408, C; 493, B) which separates it from the domical canopy. In the great majority of specimens the central tissue of the seed is not preserved and an empty sac supported from the base of the nucellus-apex occupies nearly the whole of the interior: the shrunken wall of the sac is all that remains of the large megaspore. It would seem, then, that the nucellus was almost completely destroyed as a consequence of the growth of the megaspore or embryo-sac, which eventually occupied nearly the whole of the seed-body.