Quarterly Journal of Microscopical Science, Vol s2-84, 49-72, Copyright © 1942 by Company of Biologists

Micro-Anatomical Studies on Asellus

1. The micro-anatomy of the autotomy mechanism in the thoracic appendages of Asellus is described; it shows considerable resemblance to that of Astacus, except in size.

2. The fifth thoracic pair of appendages do not autotomize in the mature male Asellus. This depends on a very small anatomical difference, the closure of a fissure which is present in the exoskeleton of normally autotomizing limbs.

3. The method of autotomy is inferred from observations, and from the arrangement of the muscles of the limb.

4. The micro-anatomical changes which accompany the very rapid expansion of the oostegites in the female Asellus, are described.

5. A system of ‘microtrichia’, probably homologous with that of insects, is described in Asellus and in certain other Crustacea. Its probable function is indicated.

6. The pattern of pigmentation in Asellus is largely determined by the muscular system of the body, but is, nevertheless, probably adaptive. The pattern in other Isopoda is similarly determined but may be modified.

7. Certain unrecorded differences between Asellus aquaticus and Asellus (Proasellus) meridianus are enumerated.