100 



HYDKOZOA. 



Fig. 47. 



(248.) The ovum developed in the ovarian vesicle is, at its first ap- 

 pearance, of a spherical shape, and imbedded in the substance where- 

 with the deciduous 

 capsule is filled (fig. 

 47, e,e'). It is sur- 

 rounded by a mem- 

 brane analogous to the 

 calyx of the ovary in 

 buds, which, being 

 torn, discovers the de- 

 nuded ovum, wherein 

 the vesicles of Pur- 

 kinje and of "Wagner 

 are easily detected; 

 but these very speed- 

 ily disappear, without 

 any other change in 

 the interior of the egg 

 being discernible. 



(249.) The next 

 step in. the process of 

 development seems to 

 be the conversion of 

 the external vitelline 

 cells into a layer, 

 situated immediately 

 beneath the vitelline 

 membrane, which may 

 be regarded as the 

 representative of the 

 blastoderm. 



(250.) The blasto- 

 derm now becomes 



thickened around the Campanularia gelaUtwsa. a a, tegumentary skeleton, or horny 



j. 11 f polypary; 6, 6', buds in progress of development into polyps ; 



VltellUS, terming a SOrt c c c , terminal polyp-cells empty; d,d',d",d'", polyps in dif- 



Of elevated ring (fig. ferenfc 8ta es of S rowth J ovarian cell containing an embryo 



. ready to escape; e', another ovarian cell containing several em- 



48, B), and the pOSl- bryos in various states of development ; /, living substance filling 



tirm nf fhp rliffprrmf the interior of the horny polypary ; ^, annular constrictions of 



ent the horny skeleton. (After Van Beneden.) 



organs hereafter to be 

 developed become recognizable. 



(251.) Certain cells now begin to make their appearance in the 

 interior of the blastoderm, the arrangement of which is particularly 

 remarkable (fig. 48, c & D, 6) ; these cells arrange themselves in groups 

 of five around the circumference of the blastoderm, and have the ap- 

 pearance of so many crystals : the form of each group is quadrilateral ; 



