No. 4-] 



BODIES OF THE INVERTEBRATES. 



^59 



room bodies occur in all Polychaeta or not ; but it is possible to 

 assert that they exist in Nereis, Lepidonotiis, and Polyn'oe. Nor 

 is it possible to aver their existence in all Crustacea ; but it is 

 certain that they occur in Cavibarus and Limulns. Both of 

 these questions will be considered at length in the final paper 

 to which is relegated a discussion of several fiber tracts con- 

 nected with the mushroom bodies. 



It is thought that sufficient facts and figures have been given 

 to demonstrate that the mushroom bodies occur in the Hexapods, 

 Decapods, Xiphosura, and certain Polychaeta. In each case these 



S.>v\ 



Fig. 6. — Sagittal section tlirough the brain of Limulns. 



bodies lie in the front portion of the supra-oesophageal gan- 

 glion. Is it not logical to conclude that the front portions of 

 these brains are homologous } This statement runs counter to 

 the generally accepted view. Goodrich,^ who has recently in- 

 vestigated this question, does not think that the homologue of 

 the Annelid prostomium, with its archicerebrum, occurs in either 

 the insects or the Crustacea. But, since the mushroom bodies 

 constitute the major portion of the protocerebrum of Hexapods 

 and Decapods, and since the mushroom bodies occur also in the 

 archicerebrum of certain Polychaeta, it follows that at least the 

 major portion of the protocerebrum of the insects and the 



1 Goodrich, E. S., " On the Relation of the Arthropod Head to the Annelid 

 Prostomium," Quart. Journ. Micr. Sci. Vol. xl, pt. ii, new series, pp. 247-268, 

 12 figs. 1897. 



