Abdominal nerves of the mature larva of castor silk moth, philosamia ricini hutt. (Lepidoptera: Saturniidae)

Abstract

Of the 8 abdominal ganglia, Ist to 6th are similar in shape and location, whereas the 7th is incompletely fused with the terminal ganglion. The interganglionic connectives are fused with each other but a median line shows their separate identity. The connectives are the shortest between the 3rd thoracic and the 1st abdominal, and between the 6th and 7th abdominal ganglia. The pattern of nerve supply is more or less similar in the 3rd, 4th and 5th ganglia, and the nerves of the 4th ganglion are considered typical. With the exception of the 7th and 8th ganglia, each gives off 3 pairs of lateral nerves, viz., transverse, dorsal and ventral, innervating dorsal and spiracular regions, dorsal and laterodorsal regions, and ventral and ventrolateral regions respectively. Union of the transverse nerve with dorsal nerve at certain points is noted in 1st, 2nd and 4th ganglia, whereas ventral nerve joins with the transverse nerve of the following segment in the 1st, 2nd, 3rd and 7th ganglia. A plexus between the transverse and dorsal nerves of the 4th, 5th and 6th abdominal ganglia is formed near their origin from the ganglia. The 7th and 8th abdominal ganglia are placed in the 7th abdominal segment, and so the nerves of the 8th abdominal ganglion travel from 7th segment to the 8th segment. The 8th or terminal ganglion gives off a pair of transverse, dorsal and fused nerves. Few branches of the dorsal nerve innervate the areas to be innervated by the ventral nerve, which is lacking in 8th abdominal ganglion. The fused nerve innervates a part of the 8th, 9th and 10th abdominal segments.