66 ZOOLOGY. 
such as the meduse of the Hydroids and the Trachy- 
nemide. In the European Nausithoe albida and Pelagia. 
noctiluca no nerve-ring is present, for this is impossible. 
owing to their deeply indented disks. There are instead eight 
Fig. 44.—Gastrula of an Aure- 
lia-like Medusa. a, primitive Fig. 45.—Scyphistoma of Aurelia 
mouth; d, gastro-vascular cavity; Jlavidula, at erent ages; magni- 
ce, ectoderm; d, endoderm.— fied.—After Agassiz, 
After Metschnikoff. 
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 
vous system in these Hydrozoa arises from the ectoderm. 
Fig. 47. — Ephyra or 
y, paren pO ew oe of 
urelia.—. r _ 
Fig. 46.—Strobila of Au- siz. Agas 
reia flavidwa. — After 
Agassiz. 
The Aurelia flavidula 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, 1877, p. 355. 
