18 



C. SASAKT. 



almost always left intact. 



Like the typical form of Anniilose animals, the nervous system of 

 the silkworm is composed of a series of thirteen ganglia connected b}' 

 two nervous cords. Each of these ganglia is enveloped by a thin trans- 

 parent membrane, and contains in its interior two yellowish masses of 

 delicate ganglion cells, each cell being provided with a large nucleus 

 {PL in, fig. 6). 



It is still uncertain by what sense the maggot is guided to the 

 ganglia. At any rate, if, after getting out of the digestive canal, the 

 maggot gets close to the ganglia (PL III, fig. 8), it soon makes its 

 Avay into them, and makes their envelopes its special covering ( PL III, 

 fig. 9). In this position it feeds on the ganglion -cells and grows larger 

 and larger until its covering ruptures, through excessive dilatation (PL 

 III, fig. Ig). 



At the time when the majj-got first o-ets lodg-ed in a ffano-lion, it 

 is ver}^ inconspicuous in size, but we may easily recognize its presence 

 with the naked eye by opening the diseased silkworms; for the ganglion 

 which harbours the maggot assumes always a white color, while those 

 which are uninjured or do not harbour the parasite is always tinged 

 light yellow. The color is in the one case simply that of the parasite 

 and in the other that of the ganglion-cells themselves. As the maggot 

 grows in size, the envelope of the ganglion gradually dilating forms a 

 sort of a membranous sac; and when this stage is reached, the diseased 

 ganglion becomes still more easy to distinguish from the others. 

 Previous to the rupture of the sac, it becomes oblong in shape like 

 the form of the contained maggot, so that the nervous cord appears 

 as if it bore a large white oblong sac in place of a ganglion ( PL III, 

 fig. 7 a). The largest maggot found in a sac of this sort measured 

 5 mm. in length. 



Generally the maggot remains in a ganglion more than a week, 



