222 KINGSLEY. [Vol. VIII. 



Nervous System. 



I leave all questions concerning the nervous system and 

 sense organs untouched, except in so far as is necessary to 

 explain some points which will appear later. I do this the 

 more willingly since my friend, Dr. Wm. Patten, has for several 

 years been devoting especial attention to this system. I find in 

 Limulus that at an early stage the nervous system, viewed from 

 the surface, presents the appearance of numerous circular pits 

 (Fig. 29). These, which are shown in section in Figs. 49 and 

 65, I suppose to be what Patten ('89 p. 602) refers to in his 

 statement that "the central cord and brain of Arthropods, is 

 at first composed entirely of minute sense organs, which in the 

 scorpion have the same structure as the segmental ones at the 

 base of the legs." Kishinouye has also seen the same struct- 

 ures and compares them to the ommatidia of the eye. There is, 

 however, no such differentiation of the nuclei as are shown in 

 the figures of the latter. Unlike Patten, I interpret these in- 

 pushings of the nuclei as centres for the rapid proliferation of 

 nerve cells, and not as sense organs. I also am inclined to 

 withdraw my original account of the formation of segmental 

 sense organs ('90), as I am now inclined to believe that the 

 structures which I described as sensory in structure (various 

 figures "jTj'") are more probably glandular. The brain arises 

 from three pairs of ganglia in front of the pair which inner- 

 vates the first pair of appendages. I believe these three ganglia 

 to represent : the first, the primitively preoral nerve centre, the 

 homologue of the "brain" of the annelids; the other two to 

 belong, like the deuto- and tritocerebrum of the Hexapod, to 

 ganglia which have left the postoral and have wandered into 

 the preoral region. Upon the real state of affairs I have, how- 

 ever, almost no actual observations, and base my opinions largely 

 upon the conditions in other groups. 



Respiratory Organs. 



As is well known the respiratory organs of Limulus are 

 borne upon five pairs of appendages situated on somites VIII- 



