STINGING-OELLS IN CRASPEDOTE MEDUS.E. 775 



digestive cells, between which are numerous characteristic 

 gland-cells Avitli coarse granular contents Avhich stain deeply. 



The first indication of a developing medusa-bud is to be 

 traced in the ectoderm, an accumulation of interstitial cells 

 causing this layer to project slightly outwards. The eudo- 

 derm soon begins to take part in this bulging out of the 

 tissues, and owes its increase in area chiefly to the prolifera- 

 tion of the large cells, but partly also to the accumulation of 

 interstitial cells, which are to be found in the endodermal 

 tissue in the region of a developing bud. These cells I 

 believe to be ectodermal in origin, for favourable sections 

 show occasional interstitial cells to migrate from the ectoderm 

 through the structureless lamella into the endoderm. In this 

 way a hollow, double-layered bud is formed (PL 43, fig. 5) 

 by a process which cannot be called one of simple evagination, 

 but in some respects resembles that of the formation of the 

 early stages of the latei-al buds in Hydra, as recently des- 

 cribed by J. Hadzi (14). 



As long ago as 1891, W. B. Hardy (15) showed that in the 

 early development of the gonophores of Myriothela 

 phrygia there was a cei'tain mixing up of endodermal and 

 ectodermal cells to form a kind of blastema, and it seems 

 probable that further investigations will prove that the pro- 

 duction of a bud from the body of a hydroid is by no 

 means so simple a process as has been made out by some 

 authoi'S. 



The entocodon is next formed by the proliferation of the 

 ectoderm at the apex of the bud, and consists of a small-celled 

 plug of tissue between ectoderm and endoderm. Four pouches 

 of endoderm are arising simultaneously from the coelenteron ; 

 from them the radial canals of the adult are to be derived. 

 Reference to fig. 6 will show that there is nothing of the 

 nature of a double- walled endodermal cup in the bud, one 

 side of the obliquely cut section showing a radial pouch, the 

 other the contact of the entocodon with the superficial 

 ectoderm. 



It is to be noticed that this superficial ectoderm has not 



