CHlRONOMUS PRASINUS. 171 



reflects light strongly, so that the larvae appear opaque and white, 

 as v/ell as knotted. This is only seen in mature larvae. 



Perhaps the most usual condition of the blood of this larva is 

 that of a clear red fluid, in which little or nothing can be 

 discerned. Frequently, however, filamentous elements (Fig. i8) 

 can be seen carried along with the circulation, and in situations 

 such as the respiratory appendages, where the movement of 

 translation is occasionally from some cause impeded ; careful 

 watching will, I think, result in the conviction that these filaments 

 have a proper movement of their own, somewhat resembling that 

 of the filaments of Oscillatorice. and knotted portions present 

 slow, amoeba-like changes of shape. On some occasions I have 

 found the blood filled with a vast number of large, clear cells, as 

 much as the r-6oo of an inch in length, having an oval outline 

 and vacuolated appearance. Whether these could be regarded 

 as blood-cells I am somewhat uncertain. 



The nervous system consists, as in Taiiypus^ of a supra- 

 oesophageal ganglion, or brain, united by a pair of crura (embracing 

 the oesophagus) with a double ganglionated cord (see Fig. 3), 

 consisting of 12 ganglia, the five anterior of which are approx- 

 imated, and the last two, closely contiguous. It may be remarked 

 that Dufour •'' states that the nervous cord of the Diptera is 

 invariably single and not double. It is evident that he either had 

 not examined the larval state of the insects, or that his statement 

 was meant to apply exclusively to the imago, in which sense it is 

 probably correct. The nervous cord of the Crane-Fly is single 

 in both conditions, but at the posterior end of each pair of 

 commissures, and immediately in front of the succeeding ganglion, 

 there is a small split in the substance of the cord, sufficiently 

 indicating that its original condition was double, as we find it in 

 TanypHs and Chiroiiomus.^ Four black pigment spots, two on 



* Recherches Anatomiques sur les Dipteres. Memoires Presentes a 

 1 Institut de France. Tome II., 1851, page 176. 



t The coalescence of the nervous cords in the perfect condition of Dipterous 

 insects must be taken, I think, as an indication amongst others of the high 

 grade of development of this order of Insects. It is paralleled by an equally 

 noticeable tendency of the integumental parts to coalesce in the ventral mesial 

 line. Compare the widely separated legs, for instance, of most, if not all, 

 Orthopterous insects with the close ap})ro.\imaiion of these organs in the 

 Uiptera. Notice also the great preponderance of the dorsal abdominal 

 plates in the latter over those of the ventral. 



