perforation thus acquires the character of a closed segmentation cavity. While the ovum itself becomes at the same time a blastosphere. [FIG. 64. LARVA OF SYCANDRA RAPHANUS AT PSEUDOGASTRULA STAGE, IN SITU IN THE MATERNAL TISSUES. (Copied from F. E. Schulze.) _me._ mesoblast of adult; _hy._ collared cells forming hypoblast of the adult; _en._ clear cells of larva which eventually become involuted to form the hypoblast; _ec._ granular cells of larva which give rise to the epiblast, which at this stage are partially involuted.] This stage nearly completes the segmentation: in the next one, the cells of the poles of the blastosphere increase in number, and the cells of the greater part of the blastosphere become columnar and ciliated, (fig. 64 _en._) while the granular cells (_ec._) increase to about thirty-two in number and appear to be (partially at least) involuted into the segmentation cavity, reducing this latter to a mere slit. This stage forms the last passed by the embryo in the tissues of the parent. The general position of the embryo while still in this situation may be gathered from fig. 64, representing the embryo _in situ_. The embryo is always placed close to one of the radial canals. From this situation it makes its way through the lining cells into a canal and is thence transported to the surrounding water. By the time the larva has become free, the semi-invaginated granular cells have increased in bulk and become everted so as to project very much more prominently than in the encapsuled state. To the gastrula stage, if it deserves the name, passed through by the embryo in the tissues of the parent, no importance can be attached. [FIG. 65. TWO FREE STAGES IN THE DEVELOPMENT OF SYCANDRA RAPHANUS. (Copied from Schulze.) A. Amphiblastula stage. B. A later stage after the ciliated cells have commenced to become invaginated. _cs._ segmentation cavity; _ec._ granular cells which will form the epiblast; _en._ ciliated cells which become invaginated to form the hypoblast.]