A. J. Grove 
17 
them, and these presumably form channels to conduct the secretion to 
the duct which leaves the gland (Plate I, Fig. 16). In the anterior pair 
this is not so marked. 
The Nervous System. 
The nervous system of the Aphides was for a long while undescribed. 
Bucktoo (1875—1882) in his monograph, entii’ely omits to figure the 
central nervous.system, as such. Witlaczil (1882) gives figures of the 
central nervous system of Aphis pelcirgonii and Pemphigius spirothecae. 
These have been very useful for comparison with that of S. rosarum. 
Mordwilko (1895) also gives an account of the nervous system of Trama 
and Lachnus. 
The central nervous system of S. rosarum, in common with the 
Aphides in general (as Witlaczil (1882) has shown), is, compared with 
that of the typical insect, greatly foreshortened, and considerable fusion 
and elimination of ganglia have taken place; and often it is only the 
distribution of the nerves which gives a clue to the identity of the 
ganglia. 
The central nervous system (Plate I, Fig. 20) consists of a series 
of ganglia comprising two cerebral or supra-oesophageal ganglia, each 
with its optic lobe or ganglion ; two sub-oesophageal ganglia; three pairs 
of thoracic ganglia; and a single median abdominal ganglion. The 
cerebral ganglia are placed in the head and are joined to the sub- 
oesophageal ganglia by the usual circum-oesophageal connectives, which 
in this case are short and stout. The sub-oesophageal ganglia are 
connected with the first pair of thoracic ganglia by what seems to 
represent a remnant of a primitive double nerve-chain. 
The three pairs of thoracic ganglia, and the median abdominal 
ganglion, are massed up together, and lie in a position between the 
insertions of the first and second pairs of legs. 
The ganglia give off nerves which pass to their respective destina¬ 
tions. 
The two cerebral ganglia, each bearing an optic lobe, occupy nearly 
the entire cavity of the head. The ganglia themselves are somewhat 
ovoid, or, better, pyriform in shape, the expanded end being directed 
towards the dorsal surface of the head, and the more attenuated end 
towards the ventral side. From the outer lateral surface of each 
cerebral ganglion arises, partly from the attenuated end, and partly 
from the lower portion of the expanded end, an optic lobe, which, seen 
Parasitology ii 
2 
