640 A. A. W. HUBBEOHT. 



missural systems" is foreshadowed at the point where brain- 

 lobe, lateral stem, and *^ vagus nerve " meet, or rather diverge. 

 It has been attempted in ligs. 1 and 2 to indicate the points 

 here alluded to in a general way, special comparisons being, on 

 the grounds that have been stated, purposely avoided. 



If we now turn to Dohrn's and Semper^s hypothesis we must 

 recognise that no such satisfactory general comparisons are 

 there possible. Even if we were inclined to accept the " turn- 

 ing over " of Geofifroy St. Hilaire, by which back and belly 

 became exchanged, and to admit the brain-piercing oesophagus, 

 regarding the Annelid supracEsophageal ganglion and the 

 ventral nerve-cord as respectively homologous to cerebrum and 

 medulla, it must still be conceded that we have not then in 

 any way before us a nerve-system offering as many points of 

 comparison with the Vertebrate system as does that of the 

 Nemertea. 



Concerning the Annelids we have no observations by which 

 the cephalic ganglia and the cephalic nerves are so clearly 

 foreshadowed, none which would throw light on the origin of 

 the vagus, its connection with the nervus lateralis and with the 

 anterior cephalic ganglia, none concerning the sympathetic 

 system and its blending with the vagus system in the lowest 

 Vertebrates, indications of which are even retained in the 

 highest. Nor is the ventral nerve-cord of Annelids, with its 

 undeniable double character and double origin a match, so 

 far as comparison goes, for the Nemertean medullary nerve, 

 with its transverse nerves preceding the spinal nerves of 

 Amphioxus and the Cyclcstomata. 



And if we are then asked to consider the lens of the Verte- 

 brate eye as a modified ectodermal branchial invagination, as 

 the outer portion of what was once a functional gill-slit,^ we 

 feel that the ground under our feet is becoming rather uncom- 

 fortable, and that it is high time to reconsider whether all 

 these ingenious speculations in which the most beautifully 

 pliable hypothetical and unknown Annelids play a too conspi- 

 cuous part should not be definitely abandoned, and a new 

 • Dobrn, 'Studien,' x, p. 459, 1885. 



