The development of the Malpighian tubules of Carausius morosus (Orthoptera)

Abstract

ABSTRACT In Carausius morosus Brunn (Phasmidae) the Malpighian tubules are morphologically and physiologically differentiated into 3 distinct types. The appendices are of unknown function, number about 31, and are inserted separately from one another over the posterior third of the mid-gut. The excretory and calciferous tubules are arranged in groups at the extreme posterior end of the mid-gut. There are 20 to 27 groups each consisting of one excretory and 5 calciferous tubules opening into a small ampulla. The tubules arise in 5, occasionally 6, generations; 2 in the embryo and one in the second, third, fourth, and sometimes in the fifth nymphal instars. The first embryonal generation is composed of the 24 to 37 appendices (pre-moult embryonal tubules), the second of the 20 to 27 excretory (post-moult embryonal) tubules. The number of calciferous (nymphal) tubules produced in each generation depends largely on the number of groups; there are usually 2 per group in the second and third instars and one in the fourth. Occasionally a single tubule is added to some groups in the fifth instar. The appendices pass backwards and are attached to the anterior parts of the hind-gut; the excretories first pass forwards, then backwards and are attached to the hind-gut just anterior to the rectum, whilst the calciferous tubules are attached distally to the fat-body. Each tubule is composed of 5 rows of spirally arranged cells which appear as hexagons in surface view. The excretory tubules are differentiated into upper and lower segments and are attached to the gut by a series of short tracheae. The calciferous tubules have a distal region filled with a white crystalline substance and are served by single spiral tracheae. The appendices are not differentiated into segments and have no tracheal supply. The development of any one tubule comprises a period of initiation and elongation by cell-division, and a period of differentiation. The first period is restricted to the first few days of a stadium, i.e. is linked to cyclical development, whilst the second continues through the remainder of the life of the insect. The secondary tubules of any one group are added alternately on either side of the first formed tubule along the line of the posterior interstitial ring, and the arrangement of tubules is a result of curvature of this ring. Tubule buds formed in a particular instar may complete their phase of cell-division in that instar or may remain dormant until the similar period in the succeeding instar. The calciferous tubules undergo a rudimentary metamorphosis in the sixth (last) nymphal stage.