64 THE LARVA OF THE BLOW-FLY. 



ganglia. The last is, however, evidently the result of the union 

 of two or more pairs. 



Each pair of ganglia gives off one, two, or three pairs of 

 nerves, and in the latter case the third pair either arise from 

 the commissures behind the ganglia, or from the posterior part 

 of the centre by a common trunk. This trunk then bifurcates, 

 and its branches unite with the anterior nerves of the succeed- 

 ing ganglion (PL II., Fig. i, al). They are the alary and 

 lateral nerves of Newport [9], and are of considerable morpho- 

 logical and physiological interest, as their origin from the 

 segmental centres is apparent rather than real, and they consist 

 of fibres, which traverse the dorsal surface of the nerve centres 

 and their commissures, and arise from the brain, so that these 

 probably represent the voluntary motor tracts of a vertebrate. 

 [Newport, 9.] 



When the primitive ganglia are fused into one or a few complex centres, 

 the determination of their exact number is exceedingly difficult. This is 

 especially the case in the Diptera. Brauer [14] gives a very complete com- 

 parative table, showing the disposition of the primitive ganglia in the larva 

 and imago of various dipterous types, in which he shows that there are 

 always three thoracic and eight abdominal ganglia. I must, however, regard 

 this table as hypothetical to a large extent although there are obviously ten 



PLATE II. THE NERVOUS SYSTEM OF THE LARVA OF THE BLOW-FLY. 



FlG. I. The Ventral Chain of the Silk Moth Larva, after Swammerdam : a, antennal 

 nerve ; ix, maxillary nerve ; eg, cephalic ganglion ; op, optic nerve ; f, frontal 

 ganglion; .r, lateral ganglia?; 2, infra-cesophageal ganglion; al, alar nerves. 

 The ganglia of the thorax and abdomen are numbered i to 10. 



FIG. 2. The Frontal and Lateral Splanchnic Ganglia of the Cockroach. After Hofer. 



FlG. 3. A Longitudinal nearly Median Vertical Section of the Neuroblast : a g, 

 antennal ganglion ; s c, stellate cell ; og, retinal disc ; n r, nerve roots. 



FlG. 4. A Median Section of the same : a s g, anterior splanchnic ganglion ; com, 

 commissure of hemispheres. 



FIG. 5- A Section through the outer part of a hemisphere : ;, retinal disc. 



FIG. 6. A Section through the crus and hemisphere. 



FIG. 7. A Longitudinal Lateral Vertical Section through the Neuroblast of the 

 newly-hatched larva. 



FIG. 8. The Ventral Ganglia of Melophagus, ist Stage, after Leuckart. 



FIG. 9. The Ventral Ganglia of Melophagus, 2nd Stage, after Leuckart. 



FlG. 10. Dorsal View of the Neuroblast : n e r, ring. 



FIG. n. Lateral View of the same : //, hemisphere ; o st, optic stalk. 



FIG. 12. Nerve Cells from Nerve Root. 



FIG. 13. Embryonic Cells of the Cortex of the Neuroblast. 



FIG. 14. Embryonic Cells and Trabeculae of the Capsule of the Neuroblast. 



