.AIKMOIK'S OK TIIK NA'IIONAI. ACADKMi OF SCIENCES. 301 



From till' imiiu'ious Iiukc gan^rlioii rolls on each sitle of thi- incdiiiu lino of the hiain, between the 

 roots of the nutlian eye nervea, is sent ott" an anterior bundle of libers (/') which passes in and 

 across the tibrous iiortion of the cerebral lobes, the libers of each bundle nieetinfj in the niitldle, 

 so as tt) inclose an inconiplj'te circle; a second set of tibers (/") behind the tirst is to lie seen 

 behind; and this is sncceeded by the transverse liliers \vlii<'h ori^rinate from the base of the 

 u'sopliajieal commissures, these libers in part orij^inatiug ti'om the basal masses of large ganglion 

 cells (I gc'). 



On the side of the main tibrous masses, scattered throughout the cortical plates of small gan, 

 glion cells, arc seen, as at in. It., the sections of irregular lateral branches of the mushroom body 

 which pass upwards from the ventral i)ortion of the brain. In this section arc also well sliown the 

 relations of the ganglia of the lirst pair of app(Midages with the libers from the (esojiliageal com- 

 missures traversing the mass of large ganglion cells, the latter sending backwards their libers, but 

 most of them sending tiliers to form the nerves to the first jiair of appendages {lut app. it.). 



In the second cut below the section just described the knife passes through the lower border 

 of the cerebral lobes, where the fibers are thrown together in tangled masses, arising from the 

 groups of large ganglion cells on each side. 



In the next cut tlie fibrous portion of the cerebral lobes is formed of two halves, which are bulb- 

 ous at their base, and in front give rise to the h>wer tegnnicntal ncivcs (PI. VIII, Fig. 1, Itu.). 



Just below this the knife passes through the scattered bundles of tibers or branches of the 

 mushroom body passing up Ir-om the under side of the brain (PI. VIII, Fig. 2). 



The brain here largely consists of plates of small-ganglion or mushroom-body cells, with portions 

 of the fibrous bundles on eiu-h side of the median line, which seem to give ri.se to the median tegu- 

 mental or hemal nerve, m. h., and larger fragments on the outer sides. Near the posterior end of 

 the brain are two masses of large ganglion cells. Just below the section just described the knife 

 passes through the plane below which no nerves are sent off, and below which there are no large 

 ganglion cells. This plane is situated between the second and lower third of the brain, and below 

 it the mass of the brain is made up of plates or sheets of small ganglion cells inclosing white or 

 fibrous masses, which pass uj) and, uniting, aid in forming the white or fibrous lobes and lobules of 

 the cerebral ganglia (PI. VllI, Fig. 4). (These plates are the lobes of the mushroom bodies.) 



Thus the tibrous portion of the cerebral ganglia are composed of fibers from the comparatively 

 few large ganglion cells and the vastly more numerous and more minute fibers emitted from the 

 small gangliiui or chromatic cells forming portions of the mushroom bodies; whether the fibers 

 from the large cells pass backwards continuously from the cerebral lobes through the ganglia com- 

 jwsing the (esophageal ring, and unite with certain tibers from the said ring to form the abdominal 

 cords, or not, is a question yet to be solved. 



Some peculiarities are to be seen in the sections of the brain of the fully grown specimens 

 (10 inches long, exclusive of the caudal spine) which are not to be observed, so far as our expe- 

 rience goes, in the smaller ones. These we will proceed to indicate. 



PI. II, Fig. 8, represents a section passing through the median eye nerve and its lobes 

 (»i. ei/c n. and in. eyrlobe) and the upper part of the cerebral lobes. The knife has passed through 

 the ends of the cerebral commissure (c com.), ensheathed, especially jiosteriorly, b>- the small gan- 

 glion cells; on each side of the central mass of large and small ganglion cells is the irregular 

 branched mass of white tibrous substance, which is small in proportion t^) the enormously devel- 

 ojied masses of small ganglion cells of the mushroom bodies, with their inclosed masses of fibrous 

 and myeloiil substance on each side. In two sections farther down, PI. II, Fig. !), the cerebral 

 eommissiue is seen on the left side to be continuous with the white tibrous matter of the left cere- 

 bral lobe, and on the right side are seen a few large ganglion cells. In the next section below, 

 the halves of the cerebral commissures are seen to touch each other ( Fig. 10) ; while in two sections 

 .still lower down (PI. Ill, Fig. 11), the commissure is complete, with its posteritu- ccutical sheath of 

 chromatic cells. The white, tibrous i>osterior region of the cerebral lobe^is now larger, and the two 

 lobes, united behind by the commissure, are anteriorly fused with the lobes of the lateral eyes 

 (Figs. 11, 12). 



Still lower down (PI. Ill, Fig. 12) this section cutting through the upper tegumental nerves 

 (u. teg. n.) the a'sophageal commissure on the right side of the brain is involved. The white por- 



