MEMOIRS OP THE NATIONAL ACADEMY OF SCIENCES. 113 



THE BRAIN OF DIPLOPOD MYBIOPODS IN GENERA! . 

 (Pis. XXIV and XXV.) 



The so called brain or snpraoesophageal ganglion of a normal-eyed Myriopod is, as in insects, 

 composed of four pairs of ganglia, viz, the antennal or olfactory ganglia, the procerebral ganglia, 

 the optic ganglia, and lastly the commissural ganglia or lobes ; the last pair of lobes being by 

 no means of the physiological importance of the others. 



Newport has described and figured the brain of the European Julus terrestris. In that species 

 the eyes are evidently rather far apart, since the author remarks that the optic ganglion " is of an 

 elongated, oval, and slightly conical form, from which nervous filaments radiate outwards and 

 downwards in a triangular fasciculus to the cornea (d)P In the brain of Spirobolus marginatus, 

 in which the eves are rather large and near together, the optic ganglia are rather short, and the 

 nerves to the facets form a conical mass, situated immediately behind the antennal nerve and 

 extending decidedly upwards, as well as outwards, the optic nerves themselves being bulbous or 

 clavate towards the facets. In Newport's figure the optic ganglia are large and about three- 

 quarters as bulky as the procerebral ganglia. Newport's description and figure of the brain of Poly- 

 desmus complanatus (Plate XXVII) show that in this and probably the entire family Polydesmidae 

 the optic ganglia, optic nerves, and eyes are entirely atrophied. No observations have yet been 

 made on any species of Lysiopetalidse with complete eyes, the family to which Pseuclotremia 

 belongs, for want of good, fresh material ; but it is probable that, as shown by the following 

 description and figures of Pseudotremia cavernarum and Scoterpes copel, the central nervous sys- 

 tem is in the same place as iu the Julidse. 



The brain and rudimentary eyes of Pseudotremia cavernarum. — The figures we present will give 

 a better idea of the relatiou of parts than any description we can give. By referring to the 

 longitudinal sections* (PL XXV, figs. 3 and 4) through the head of Pseudotremia one will perceive 

 the relations of the braiu to the rest of the head. Fig. 3 represents a section through the middle 

 of the head, passing through the procerebrum (pel.) and the subcesophageal ganglion and suc- 

 ceeding nervous tract, also the mouth and oesophagus. In Fig. 4 the section passes through one 

 side of the head, involving several facets of the eye, the antennal lobe, and its nerve. In eighty 

 longitudinal sections of the entire head of one specimen and thirty-two of another no traces of the 

 optic nerves were to be seen, the rudimentary eyes being separate from the optic ganglia. 



Transverse sections of two heads were made, one hundred and twenty-two of one and one 

 hundred of the other. Iu none of them were any traces of the optic nerves discovered. Figs. 

 6 and 7 represent transverse sections of the brain, showing the well-developed olfactory lobes and 

 the commissural lobes, but the sections in front show no traces of the optic lobes. 



Of eighty horizontal sections of the head, passing from above downward, Figs. 9 and 10 repre- 

 sent the most instructive sections of the brain. In the section represented by Fig. 9 the eye is 

 cut through and the procerebrum aud optic ganglion of the left side shaved ; the section also 

 involves the suboesophageal ganglion. Fig. 10 represents a section a little lower down, through 

 four of the facets aud the end of the optic ganglion. Neither in this nor the succeeding sections 

 could the optic nerve be perceived, unless a few nerve fibers passing through a small mass of 

 myeloid substance (" puntzsubstantz ") at op. n. ? be regarded as the remains of an optic nerve. It 

 will be observed that the elongated conical end of the optic ganglion terminates very near the 

 nearest facet, the substance of the ganglion consisting of ganglion cells and very few fibers sit- 

 uated at the apex of the conical mass. 



The relation of the optic ganglion to the rudimentary eye and the absence of the optic nerve 

 may be further seen by an inspection of the section succeeding that represented by Fig. 10 (Fig. 

 11). The optic ganglion ends in a point nearly in contact with the nearest facet, but, as may 

 be seen by Fig. 11a, the end of the ganglion consists of a cortical layer of ganglion cells (go.) 

 pressing agaiust the dark hypodermis {hyp.), while within is the myeloid substance (my.) with scat- 



* I am indebted to Prof. H. C. Bumpus for sections oi" l'ooudotromia aud Sootorpes, as well as of the Crustacea, 

 described in this paper. 



8. Mis. 30, pt. 2 8 



