vii NERVOUS SYSTEM OF MEDUSA 341 



also verified, that the formation of a definitely circumscribed 

 brain will take place by the gradual concentration of nerve- 

 cells at one or several points of the body which are most 

 exposed to contact with the external world, and on which 

 therefore the sense organs develop. These conclusions were 

 verified both by the anatomical and the physiological 

 investigation. 1 



The central nervous system of Beroe ovatus' consists of 

 nerve-cells which lie beneath the delicate epidermis of thin flat 

 epithelial-cells, which are distributed over the whole surface 

 of the body, but are accumulated in larger numbers at the 

 closed end of the sac-shaped body in the neighbourhood of 

 the sense organ there situated. At this spot the nerve-cells 

 form externally a sense - ganglion, and beneath that the 

 rudiment of a definite brain formed of aggregated nerve-cells. 

 But the nerve-cells scattered over the whole surface are con- 

 nected by delicate nerve-fibrils on one side with the epidermis- 

 cells, on the other with the muscle-fibres which traverse the 

 gelatinous tissue (neuromuscular fibres). 



The nervous system of the great Scyphomedusae, the 

 toponeurous Medusae, is, according to my anatomical re- 

 searches, first published in 1877, but suggested in 1873 by 

 my section experiments, 2 similarly constructed ; but the 

 accumulations of nerve-cells which represent brains are here 

 found chiefly on the edge of the bell, again in the neighbour- 

 hood of the sense-organs. Brains connected by a ring-nerve 

 are formed in the same position in the cycloneurous Medusae, 

 and their cells and fibres are demonstrably formed of ectoderm 



1 Cf. Th. Eimer, Versuche iiber kilnstliche Theilbarkeit von Beroe ovatus, 

 angestettt zum Zweck der Controle seiner Morphologischen Befunde uber das 

 Nervensystem dieses Thieres, Arch./, mik. Anat. Bd. xvii. 1879. 



3 Sitzungsberichte der physikalisch-medicinischen Oesellschaft zu Wiirzburgfiir 

 das Gesellschaftsjahr 1873-74, Part ii., erste Sitzung am 13 Dez. 1873 ; and 

 Ueber kilnstliche Theilbarkeit von Aurelia aurita und Cyanea capillata in 

 physiologische Individiien, etc., Verh. der phys.-med. Oes. zu Wilrzb. N.F. Bd. v. 

 1874. 



