MEJIOIKS OF THE NATIONAL ACADEMY OF SCIENCES. 301 



From the numerous large gaugliou cells on each side of the median Hue of the brain, between the 

 roots of the mediau-eye nerves, is sent off an auterior bundle of fibers (/') which passes in and 

 across the fibrous portiou of the cerebral lobes, the fibers of each bundle meeting in the middle, 

 so as to inclose an incomplete circle; a second set of fibers (/") behind the first is to be seen 

 behind; and this is succeeded by the transverse fibers which originate from the base of the 

 ttsophageal commissures, these fibers in part originating from the basal masses of large ganglion 

 cells (l g C). 



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

 glion cells, are seen, as at m. b., the sections of irregular lateral branches of the mushroom body- 

 which pass upwards from the ventral portion of the brain. In this section are also well shown the 

 relations of the ganglia of the first pair of appendages with the fibers from the oesophageal com- 

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

 most of them sending fibers to form the nerves to the first pair of appendages {1st app. n.). 



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 lower tegumental nerves (PI. VIII, Fig. 1, Itn.). 



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

 mushroom body passing up ttom 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 each side of the median line, which seem to give rise to the median tegu- 

 mental or hemal nerve, m. «., 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 up and, uniting, aid in forming the white or fibrous lobes and lobules of 

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



Thus the fibrous 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 ganglion 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- 

 posing the oesophageal ring, and unite with certain fibers 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 

 (m. eye n. and m. eye-lobe) and the upper part of the cerebral lobes. The knife has passed through 

 the ends of the cerebral commissure (c. com.), ensheathed, especially posteriorly, by 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 fibrous substance, which is small in proportion to the enormously devel- 

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

 and myeloid substance on each side. In two sections farther down, PI. II, Fig. 9, the cerebral 

 commissure is seen on the left side to be continuous with the white fibrous matter of the left cei-e- 

 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 posterior cortical sheath of 

 chromatic cells. The white, fibrous posterior region of the cerebral lobes 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 

 (M. teg. n.) the oesophageal commissure on the right side of the brain is involved. The white por- 



