ND. 1788. 



NORTH AMERICAN ERGA8ILIDJE— WILSON. 



295 



fused, and extend to the eye, 

 striking the latter at the level 

 of the ventral surface of the 

 two dorsal ocelli. The cellular 

 elements form a thick super- 

 ficial layer over the posterior 

 two-thirds of the gangUon, 

 then become abruptly scanty, 

 the optic nerves being com- 

 posed almost wholly of fibers, 

 with only a very few scat- 

 tered nuclei among them. The 

 whole center of the ganglion 

 is a broad ribbon-like mass of 

 fibers. The nuclei are also ab- 

 sent from the lateral and dor- 

 sal surfaces at the posterior 

 end where the ganglion passes 

 into the commissures, and this 

 portion shows exclusively a 

 fibrous structure. Some of the 

 fibers can be seen to cross 

 fTom one commissure to the 

 other, or from the commissure 

 on one side diagonally to the 

 ganglion on the opposite side, 

 but there is apparently no 

 definite grouping of either the 

 fibers or the nuclei. From the 

 anterior end of the ganglion, 

 on either side of the optic 

 nerves, are given off the nerves 

 to the first antennae, which run 

 forward just outside of the 

 lateral ocelli. At the point of 

 their origin the ganglion is 

 somewhat swollen laterally and 

 contains a number of nuclei. 



From the dorsal surface of 

 the ganglion, just in front of 

 the stomach, arise the two 

 short frontal nerves which 

 supply the anterior portion of 

 the head, the so-called frontal 



region. 



From either side of the gan- 

 glion, a little posterior to the 



Fig. 15.— Median longitudinal section of Erga- 



SILUS CENTRARCHIDARUM. 0, ANUS; am, MUSCLES OF 



SECOND antenn.e; d^, digestive gland; dm, dorsal 

 muscles; e, eye; g' to g'^-, ganglia of thoracic and 

 genital segments; gc, gland cells; i, intestine; 

 I, lacuna; m, mouth; n. ventral nerve cord; 

 0, anterior end of ovary; a, esophagus; p, pro- 

 tractor muscles of stomach; sbg, post (sub) 

 esophageal ganglion; spg, vrm (supra) esoph- 

 ageal ganglion; sr, semen receptacle; st, stom- 

 ach; up, UTERINE process OF OVARY. 



