I08 WHEELER. [Vol. VIII. 



Concerning the researches of Cholodkowsky on the brain of 

 Blatta germauica, I must say a few words, since I have de- 

 scribed the brain and nerve-cord of this form as agreeing in all 

 essential respects with those of XipJiidunn. Cholodkowsky lays 

 great stress on the existence of three distinct pairs of Pimkt- 

 siibstanz masses in the supraoesophageal ganglion as indicat- 

 ing the presence of three segments. When we come to exam- 

 ine his figures we find that he takes a very unusual view of 

 brain-segmentation, for the three pairs of Punktsubstanz masses 

 are seen to belong (Fig. 46 PI, IV; Fig. 6^ PI. VI) to the 

 protocerebrum and correspond to the centres of its three lobes. 

 He did not distinguish the deuto- and tritocerebral segments ! 

 Such of his remarks on the development of the brain and 

 ventral nerve-cord as are at all comprehensible show similar 

 glaring defects in observation. Thus he has failed to detect 

 the small dermatoblastic cells which from the first cover the 

 brain and nerve-cord. He asserts that these organs are at first 

 naked and are only subsequently covered by an overgrowth of 

 the integument from the sides of the body. The antennal and 

 neural furrows do not play the part in development that he 

 ascribes to them. The last abdominal ganglion of the mature 

 embryo does not consist of four but of three fused ganglia; 

 the fusion of the second and third abdominal ganglia was com- 

 pletely overlooked. 



3. General Remarks on the Nervous System. 



The nervous system of Arthropods is by common consent 

 derived from the nervous system of annelid-like forms, and it 

 is to this group that we naturally turn in seeking an explanation 

 for certain structures in the Hexapod brain and nerve-cord. 



In a brief preliminary paper Patten ('88) made the statement, 

 that " the ventral cord and brain of Arthropods is at first 

 composed entirely of minute sense-organs, which in scorpions 

 have the same structure as the segmental ones at the base of 

 the legs." This would seem to indicate that the Arthropod 

 nervous system can be traced back to the condition seen in 

 Polychaeta — LopadorhyncJms, according to Kleinenberg ('86) — 

 where both brain and nerve-cord arise in connection with and 



