382 MONTGOMERY. [Vol. XIII. 



the distribution of the neuroglia, and of the ganglion cells II 

 and IV, as well as the one or two posterior commissures of 

 the ventral brain lobes, hitherto undescribed, have also been 

 studied to a certain extent. 



To the central nervous system of the nemerteans must be 

 reckoned: (i) the dorsal and ventral brain lobes and their com- 

 missures; (2) the lateral nerve chords which, in both species 

 examined, here unite posteriorly just beneath the end of the 

 posterior intestine; (3) the paired oesophageal nerves; (4) the 

 longitudinal nerves of the proboscis (two in number in each of 

 our species); (5) the dorsal, unpaired, larger, median nerve of 

 the body wall ; and probably also (6) the lesser, unpaired, median 

 nerve. Thus in the nemerteans the central nervous system, 

 i.e., that portion of the whole nervous system with which 

 ganglion cells are in contact, has an extent and diversification 

 which closely approach that of the Mollusca. Previous authors 

 have limited the term " central nervous system " to the brain 

 lobes and lateral chords, disregarding the fact that the other 

 parts, mentioned above, are also provided with ganglion cells. 

 My own investigations have been limited to the brain lobes, 

 lateral nerve chords, and oesophageal nerves. 



Before the appearance of MTntosh's monograph ('73), no 

 studies had been made upon the elements of the nervous system 

 of the nemerteans. Since that time a considerable number of 

 investigations have been published, only the more important of 

 which will be specially mentioned here. Reference may be 

 made to the papers of M'Intosh ('75, '76), Hubrecht ('74, '75, '79, 

 '80, '87a, '87b), Mosely ('76), V. Kennel ('77), v. Graff ('79), Gul- 

 liver ('79), Dewoletzky ('80, '88), Salensky ('84, '86), Vogt and 

 Yung ('85), Bateson ('86), Burger ('88, '90a, '90b, '91a, '91b, '94a, 

 '95), Haller ('89), Joubin ('90, '94), Dendy ('92), and Coe ('95a, '95b). 



It is, however, v. Kennel, and more especially Hubrecht and 

 Burger, who have added most to our knowledge of the nervous 

 system of the nemerteans. Hubrecht had especially studied the 

 differentiation of the nervous system in its various layers, and 

 had described the course of the larger nerves, etc. ; he studied 

 to less extent the cytological structure. Burger considered not 

 only the anatomy, but also the finer structure of the elements 



