406 INVERTEBRATA. 



BIBLIOGRAPHY. 



Origin of the Nervous System. 



(316) F. M. Balfour. "Address to the Department of Anat. and Physiol. of the 

 British Association." 1880. 



(317) C. Claus. " Studien lib. Polypen u. Quallen d. Adria. I. Acalephen, 

 Discomedusen." Denk. d. math.-naturwiss. Classe d. k. Akad. IViss. Wien, Vol. 

 xxxvin. 1877. 



(318) Th. Eimer. Zoologische Studien a, Capri. I. Ueber Beroe ovatus. Ein 

 Beitrag c. Anat. d. Rippcnquallen. Leipzig, 1873. 



(319) V. Hensen. "Zur Entwicklung d. Nervensystems." Virchcnv's Archiv, 

 Vol. xxx. 1864. 



(320) O. and R. Hertwig. Das Nerven system u. d. Sinnesorgane d. Medusen. 

 Leipzig, 1878. 



(321) O. and R. Hertwig. "Die Actinien anat. u. histol. mit besond. Beriick- 

 sichtigung d. Nervenmuskelsystem untersucht." Jenaische Zeit., Vol. xm. 1879. 



(322) R. Hertwig. " Ueb. d. Bau d. Ctenophoren." Jcnaische Zeitschrift, 

 Vol. xiv. 1880. 



(323) A. W. Hubrecht. "The Peripheral Nervous System in Palaao- and 

 Schizonemertini, one of the layers of the body-wall." Quart. J. of Micr. Science, 

 Vol. xx. 1880. 



(324) N. Kleinenberg. Hydra, due aiiatomisch-cnt-cvickhmgsgeschichtliche Un- 

 tersuchung. Leipzig, 1872. 



(325) A. Kowalevsky. " Embryologische Studien an Wiirmern u. Arthropo- 

 den." Mem. Acad. Pctersbourg, Series vn., Vol. xvi. 1871. 



(326) E. A. Schiifer. " Observations on the nervous system of Aurelia aurita." 

 Phil. Trans. 1878. 



Nervous system of the Invertebrata. Our knowledge of 

 the development of the central nervous system is still very 

 imperfect in the case of many Invertebrate groups. In the 

 Echinodermata and some of the Chaetopoda it is never detached 

 from the epidermis, and in such cases its origin is clear without 

 embryological evidence. 



In the majority of groups the central nervous system may be 

 reduced to the type of a pair of cephalic ganglia, continued pos- 

 teriorly into two cords provided with nerve-cells, which may 

 coalesce ventrally or be more or less widely separated, and be 

 unsegmented or segmented. Various additional visceral ganglia 

 may be added, and in different instances parts of the system 

 may be much reduced, or peculiarly modified. The nervous 

 system of the Platyelminthes (when present), of the Rotifera, 

 Brachiopoda, Polyzoa (?), the Mollusca, the Chaetopoda, the 



