308 Royal Society : — 



M. Ramdohr examined C. Alni, but his description can hardly be 

 correct, since it is scarcely possible that nearly allied species can 

 differ so entirely in the arrangement of such important organs. 

 Unless Coccus Alni does differ very much from C. hesperidum, he has 

 made the same mistakes as M. Leydig, with the addition of having 

 misunderstood or overlooked the hepatic glands, which perhaps he 

 may have mistaken for ovaries. 



The intestinal canal of C. Persicce is formed on the same type as 

 that of C. hesperidum. 



Nervous System. 



I do not propose to give a detailed account of the nervous 

 system, and only allude to it in order to mention the great variations 

 observed in different specimens. Figs. 2-9 represent different forms 

 of the nervous system in C. hesperidum, and fig. 10 that of C. Per- 

 sic(e : in all, the objects are magnified 60 diameters. 



Leydig rightly describes the suboesophageal portion of the gan- 

 glionic column as being reduced to a large mass (fig. 2, &c. A), 

 situated close behind the mouth. This ganglion generally emits, 

 besides the commissure, three large nerves on each side, and its 

 hinder extremity is continued into a still larger nervous column (C), 

 which passes backward for rather more than -014 of an inch without 

 throwing off any branches. It then divides, and after a while each 

 of the divisions again subdivides, so as to give off a rich plexus of 

 nerves to the posterior part of the body. 



The posterior pair of nerves (fig. 2, &c.) always throws off on its 

 inner side, and not very far from its origin, a nerve (F) which I 

 once traced and found to unite with one of the nerves derived from 

 the main central chord. This nerve (F) is always present ; but the 

 point at which it leaves the main nerse (B) is very variable, being 

 sometimes as much as '014 of an inch from the suboesophageal 

 ganglion, sometimes quite close to it. Indeed, in more than one 

 instance it arose from the ganglion itself, and not from the nerve B 

 (fig. 3). 



In the divisions also of the central stem there are very great 

 variations, which it would be endless to describe in detail. Perhaps 

 the arrangement most generally met with, and that which I am 

 inclined to regard as the type, on account of its presenting the 

 nearest approach to symmetry, is that the main central chord sepa- 

 rates, at about -014 from its origin, into two equal branches, and 

 these again, after a course of about "Ol, divide dichotomously 

 (fig. 2). In such a case the division of F from B generally takes 

 place at a considerable distance from the ganglion. 



I have, however, not met with many specimens presenting even 

 this very limited amount of symmetry and regularity. 



In fig. 4 we see the two divisions (G, G) of the central chord C 

 divide almost immediately and yet not symmetrically. In fig. 5 the 

 chord C divides into two unequal divisions, the smaller of which 

 passes along for more than 'OM before it redivides, while the larger 

 branch divides into three at a point only '006 from its origin. 



