SUMMARY

We have brought together under the name of sexual coaptalion various anatomical systems wich are associated morphologically and physiologically :

1. The copulatory organs of the Æ£uoniscoïdea : The genital apophysis (= penis) and the endopods of the first pair of pleopods ; the endopods ofthe second pair of pleopods ; and the exopods of the fifth pair.

2. We also include secondary sexual charaters which are borne by two successive articles of the seventh leg of the males of certain species and which appear as a prehensile pincer. |

There exists a coaptation between the genital apophysis and endopods in Trichoniscidæ. It presents in the superior Ontiscoïdea (Embolophora of Vernogrr) a progressive evolution, from the Scyphacidæ to the Armadillideæ. The terms of Vermorrr, Endophora and Embolophora, which are based on anatomical errors, must be replaced by the terms Synocheta (fused vasa deferentia) and Crinocheta (separate vasa deferentia) to designate the two superfamilies of Zuoniscoïdea.

This coaptation is doubled in certain genera of the two superfamilies by a coaptation which joins directly endopods 1 and which functions in an analogous manner. +

Endopods 2 are present, while at rest, in a closed gutter along the internal border of exopod 5.

The secondary sexual characters which constitute together the prehensile pincer of pereiopod 7 of certain species are found separately, in numerous neighbouring species.

Comparative anatomical studies and the study of the actual functioning of these coaptations in the various families allow us to state the following Res :

. The structures vil compose most of these coaptations exist quite separt in certain species.

. The coexistence of these structures does not necessarily 1m DD the realia of a coaptation.

3. Those coaptations wbich seem indispensable exist in all species and present a progressive evolution ; those coaptations whose utility appears very problematical are rare, and have a feeble evolution followed by a total regression.

Study of the development and the formative mechanism of these coaptations shows that each of the complementary organs which constitute the coaptation is formed independently, but that at moulting the coaptation, at first rather coarse, is transformed into a precise coaptation by interaction of the soft and plastic organs followed by the laying down of chitin. This interaction adapts the outlines and creates new details which do not always belong to the coaptation itself.

Experimental creation of a coaptation confirms the above results.

Certains coaptations are destroyed after their formation because of growth allometries of the two complementary organs.

A rapid review of the coaptations which have been described by various authors in other groups of animals (Insects, Crustacea, Arachnids, Molluscs) shows a confirmation of the above results.

The formation of a coaptation may be considered as resulting from he coexistence of details which appeared separately, and generally at the same position in certain species — homologous mutations.

It is also possible that certain coaptations may have been formed as the result of a single mutation which modified a preexisting detail while at the same time it brought out the complementary detail.

Darwinian selection is the only theory which leads us to understand in a rational way how such a structure as a coaptation, which can be immediately functional, may be preserved and evolve progressively ifit is useful, while it may on the contrary regress in ontogeny or phylogeny if it is useless.