€6 



ZOOLOGY. 



sncli as the mednsaj of the Hydroids and the Tracliy- 

 tiemida. In the European Xa us if hoe alhida and Pelagia 

 noctiluca no nerve-ring is present, for this is impossible 

 owing to their deeply indented disks. There are instead eight 



Fig. 45. — Scyphistoma of Avrelia 

 fiavidvla, at different ages; magm- 

 flcd.— Af tCT / 



Pie. 44— Gastrala of an Atire- 

 lia-like ^fedu8a. a. primitivo 

 month ; 6, gastro-Ta.>icnlar cavity; 

 c. ectoderm ; d, endodenn. — 

 After Metsclmikoff. 



separate nerve- tracts which unite with the sense-organs in a 

 special elevation of the edge of the disk, forming so-called 

 sense-bearers, which alternate with the eight tentacles. 

 Aurelia aurita has a similar disconnected nerve system.* 



Eimer confirms these discoveries, and states that the ner 

 Tons system in these Hydrozoa arises from the ectoderm. 



Fig. 415.— Strnbila of Au- 

 rdia- Jiavidula. — After 

 Aga;-- Iz. 



Fig. 47. — Ephyra or 

 e:irlie!;t free condition of 

 A urelia. — After Agas- 



siz. 



The Aurelia fiav id ula spawns in late summer, the females 

 being distinguishable by their yellowish ovaries, the male 

 glands being roseate, while the tentacles of the females are 



* Jenaische Zeitschrift, 18TT, p. 355. 



