On the Morphology of the Compound Eyes of Arthropods

Abstract

In studying the structure of the ommatidium of the compound eye of Serolis it has been found that it may be reduced to a simple ectodermic invagination of the skin. Extending my researches over several other Arthropods, of which Talorchestia, Cambarus, Homarus, and Callinectes were mentioned in the preceding pages, the same interpretation of the ommatidium may be applied without exception. This view of the ommatidium finds its strongest support in the fact that in Limulus the ommatidium is an open pit of the skin. By supposing that the ommatidial pit of Limulus became deeper, and that this was accompanied by modifications in the structure and arrangement of the component cells, we can show the probability of our first supposition that the ommatidium of the compound eye of an Arthropod is an independent invagination of the skin. If this view is correct, the unit of the compound eye of an Arthropod is not, after all, so complex a structure as has been supposed by some; and the enormous increase in the number of ommatidia in a given area of the skin which results in the formation of the compound finds its parallel in the well-known method of the formation of the morphological organs, viz. the duplication of a simple unit.