140 A. HAMMOND ON A COMPARISON OF THE METAMORPHOSIS 



what general indications to be found in Shuckhard's translation 

 of " Burmeister" may have afforded me. This larva is a footless 

 maggot, measuring nearly an inch in length, and consisting, I 

 believe, of 17 segments, of which five constitute the head, three 

 the thorax, and nine the abdomen. The five segments, which 

 together constitute the head, are consolidated into a rigid, horny 

 case, of which the major portion, which I regard as the 5th 

 or optic segment, is withdrawn within the softer integument 

 of the succeeding thoracic ones. The four remaining segments, 

 viz., those bearing the antennae and the tropin, are external, 

 not beinsr included in the invagination referred to. The head 

 thus formed, when seen from below, is shaped somewhat like a 

 bishop's mitre, having a deep cleft clown the centre of the in- 

 ternal portion, through which the oesophagus, the dorsal vessel, 

 and the cephalic nerves pass ; it is occupied in great part 

 by the large muscles of the mandibles, the eyes being absent. 

 A system of longitudinal and transverse muscles clothes the whole 

 internal surface of the integument, with the exception of a narrow 

 strip in the central line of the dorsal and ventral surfaces, in the 

 former of which the dorsal vessel, and in the latter the nervous 

 cord lies. Respiration is conducted by means of two main trachea?, 

 opening near the anus. These extend the whole length of the 

 larva, but instead of terminating, as in the maggot of the Blow 

 Fly, in two anterior spiracles, they break up abruptly into a number 

 of branches, of which some enter the head, while others proceed 

 to the imaginal discs, and the muscles of this portion of the body. 

 The nervous system consists of a single nervous cord, with twelve 

 ganglia, two of which belong to the head, three to the thoracic, 

 and seven to the abdominal segments. Of the cephalic ganglia, 

 one lies above the oesophagus, and the other beneath it. Bur- 

 meister regards these as the cerebrum and cerebellum respectively. 

 From the former proceed the optic and antennal nerves, and from 

 the latter those of the trophi. The three next, or thoracic ganglia, 

 and the first abdominal, present in their close approximation, what 

 seems an approach to the condition manifested in the Blow Fly, 

 where the whole of the nervous system is collected in the anterior 

 segments. These ganglia, together with the remaining abdominal 

 ones, send out each two pairs of nerves, one from their superior 

 and one from their inferior surface. 



I must now speak of those structures found in the adult larva, 



