The Internal Anatomy of the Silverfish Ctenolepisma campbelli and Lepisma saccharinum (Thysanura: Lepismatidae)1

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Abstract
The several organ systems of these two species are described, compared, and illustrated. Differences were found in the tracheation of the eye, the disposition of vestigial stylal tracheae, and the absence in L. saccharinum of the ventral tracheal commissure of the eighth abdominal segment. The digestive system follows a generalized plan, similar to that of Orthoptera. In C. campbelli, but not in L. saccharinum, the first five abdominal ganglia have migrated one segment forward, but each continues to innervate the segment from which it came, whether a tracheal connection with that segment is preserved or not; the different behavior of tracheae and nerves in relation to such migrated ganglia seems a result of the sequence of their formation in the embryo. In both species the dorsal vessel is pulsatile for its whole length, but little or no peristalsis was observed; instead, systoles occur alternately in an anterior and a posterior chamber which are separated by a thoracic valve. Ten pairs of ostia were observed with difficulty through the transparent integument of living C. campbelli; probably those of L. saccharinum are similar. Pericardial cells were less numerous in the former than in the latter species. Each ovary consists of five ovarioles, connected to a common duct near the base of the ovipositor; the spermatheca lies beneath the eighth abdominal ganglion and communicates with the oviduct, ovipositor, and genital pore above the eighth sternite. Males have three pairs of testes on each side of the body, each pair discharging through a common vas efferens into a vas deferens which leads to one of the two seminal vesicles; and from this a long tube, with accessory glands apparently built into it, runs to the base of the acdeagus. Apical cells, not previously known in Thysanura, were found present in the testes. Histological sections of the aedeagus and its base provide, for the first time, evidence for a paired origin of this organ in Apterygota.

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