ZOOLOGY. 



4. Blastostyles and Gonothecae. When an erect stem 

 has reached its full development it produces special repro- 

 ductive zooids in the axils of the peduncles of the ordinary 

 zooids. These arise by gemmation, and have the form of 



TENTACLE 



Fig. 198. LONOITUD:ML SECTION OF A HYDROS Zoom HIGHLY MAGNIFIED. 



narrow cylindrical tubes closed at the outer end. They 

 are therefore zooids, without either mouth or tentacles. 

 They are contained in special capsules formed of perisarc. 

 These capsules are called gonothecae, and have an elegant 

 shape like that of an ancient amphora, with a short narrow 

 neck ending in an aperture. The blastostyle gives rise to 

 a considerable number of lateral buds, which develop into 

 medusae. Each bud at first is a simple process of the wall 

 of the blastostyle, and the manner in which it becomes a 



