Fig. 1.

Anatomy of the crustacean CNS and swimmeret system. (A) Drawing of a prawn viewed from the left side that shows five pairs of swimmerets (arrowheads) on the ventral side of the abdomen (from Huxley, 1880). (B) Drawing of the crayfish nervous system, viewed from the dorsal side (modified from Keim, 1915). The third abdominal ganglion, A3, is labeled. (C) Drawing of a pair of swimmerets, viewed from the front, with their innervation and musculature exposed (modified from Keim, 1915). The nerve that innervates each swimmeret (N1) extends from the segmental ganglion (A3) to the swimmeret's muscles and sense organs. (D) A view from the midline of the right half of one segment of a dissected lobster abdomen (modified from Davis, (1968c). The main abdominal flexor and extensor musculature has been removed to expose some of the swimmeret muscles located in the lateral abdomen. A3: Abdominal ganglion 3. N1: Nerve projecting from A3 to the swimmeret (SW). PS: two power-stroke muscles. RS: a return-stroke muscle. Anterior is to the left; dorsal at the top. (E) A more detailed view of the innervation of a swimmeret, viewed from the same perspective as D. The anterior branch (N1a) and posterior branch (N1p) of the swimmeret nerve branch repeatedly to innervate individual PS and RS muscles and turn to enter the swimmeret itself (SW). In this drawing, modified from Davis (1968a), one large PS muscle has been cut away to reveal the nerves beneath it.