258 PEOFESSOR F. M. BALFOUR. 



give rise to a pair of nerve-cords united in front and behind 

 — exactly such a nervous system, in fact, as is present in many 

 Neinertines (the Enopla and Pelagonemertes), in Peripatus 

 and in primitive molluscan types (Chiton, Fissurella, &c.). 

 From the lateral parts of this ring it would be easy to derive 

 the ventral cord of the Chaetopoda and Arthropoda. It is 

 especially deserving of notice, in connection with the nervous 

 system of the above-mentioned Nemertines and Peripatus, 

 that the commissure connecting the two nerve-cords behind 

 is placed on the dorsal side of the intestines. As is at once 

 obvious, by referring to the diagram (fig. 231 b), this is the 

 position this commissure ought, undoubtedly, to occupy if de- 

 rived from part of a nerve-ring which originally followed more 

 or less closely the ciliated edge of the body of the supposed 

 radiate ancestor." (' Comparative Embryology/ vol. ii, pp. 

 311,312.) 



The facts of development here recorded give a strong addi- 

 tional support to this latter view, and seem to render possible 

 a considerable extension of it along the same lines.] 



[The editors of the present memoir intend to prepare for 

 publication a complete monograph of all the species of Peri- 

 patus known, with figures in extension of the materials for 

 that purpose collected by the late Prof. Balfour. They would, 

 therefore, feel extremely obliged for the loan of any specimens, 

 especially of species from the West Indies. Such specimens 

 would be most carefully preserved from injury, and returned 

 after inspection and comparison. Any such should be sent to 

 Mr. A. Sedgwick, Trinity College, Cambridge.] 



List of Memoirs on Peripatus. 



(1) M. Lansdown Guilding. — " An Account of a New Genus of Mollusca," 



' Zoological Journal,' vol ii, p. 443, 1826. 



(2) M. Andouin and Milne-Edwakds. — " Classific des Annolides et descrip- 



tion le celles qui liabitent les cotes de France," p. 411, ' Ann. Scien. 

 Nat.,' ser. i, vol. xxx, 1833. 



