582 WILLI A.M PATTEN. 



the antennae which develop from the second pair of ganglia 

 are homologous with the second pair of crustacean antennae ; 

 structures corresponding to the first pair of crustacean an- 

 tenuEe are not developed in insects. Our knowledge of the 

 development of the brain in Crustacea is as yet so imperfect as 

 to forbid any comparison between its development and that of 

 insects. I hope, however, to be able to make some investiga- 

 tion on this subject from a comparative point of view. 



A cross section of the brain, perpendicular to the anterior 

 surface of the head, discloses a pair of solid rod-like ingrowths 

 of the ectoderm, which form a part of the endocranial support 

 for the brain (PI. XXXVIb, fig. 16) . There is no infolding at the 

 surface to mark their points of origin. A second pair is shown 

 in sections dorsal and parallel to that just described ; they 

 originate from the posterior wall, and project forward and 

 inward (PI. XXXVIb, fig. 15). 



Bridging a broad and deep invagination of ectoderm in 

 the middle of the anterior face of the head, there is developed 

 a low conical structure with a sharp apex. It is the same 

 organ described by Zaddach as an apparatus used in rupturing 

 the chorion at the time of hatching (PI. XXXVIb, fig. 15, c). 



A very remarkable club-shaped organ lies just beneath the 

 structure just described ; at its lower end it is somewhat 

 narrowed and is attached to the anterior surface of the brain ; 

 from this point it projects upward into the narrow space 

 between the brain and its chitinous wall, and there terminates 

 freely. It is bounded on each side by an infolded portion 

 of the ectoderm, which forms a part of the endocranium. 

 When seen in section (PI. XXXVIb, fig. 15, b) it appears 

 like a tube whose wall is thrown into folds, the centre 

 being occupied by a clearer and less granular substance. 

 These two peculiar organs, which appear to stand in intimate 

 relation with one another, I regard as the rudiments of the 

 simple eye, the so-called '^egg-rupturing apparatus " being 

 the modified lens (?) whilst the club-shaped organ beneath is a 

 special nerve centre, corresponding to the ring-like structures 

 seen, according to Leydig, in the brain of ants. If, according 



