. Evolution and disease . type. Atavistic phenomena of this character arc not un-known in the animal world, some of which we will nowconsider. One of the most remarkable recorded examples ofthis form of atavism occurred in a rock-lobster {Paliimriispenicillatus). It is the specimen originally described byM. Alphonse Milne-Edwards, and referred to by Darwin ;the drawing has been published by Professor G. (fig. 77). Notwithstanding the differences observed in thevarious appendages of lobsters, such as the antennas,eye-stalks, swimmerets, chelai, and the like, morpho- 140 EVOLUTION AND DI
. Evolution and disease . type. Atavistic phenomena of this character arc not un-known in the animal world, some of which we will nowconsider. One of the most remarkable recorded examples ofthis form of atavism occurred in a rock-lobster {Paliimriispenicillatus). It is the specimen originally described byM. Alphonse Milne-Edwards, and referred to by Darwin ;the drawing has been published by Professor G. (fig. 77). Notwithstanding the differences observed in thevarious appendages of lobsters, such as the antennas,eye-stalks, swimmerets, chelai, and the like, morpho- 140 EVOLUTION AND DISEASE. legists hold the opinion that all these appendages aremodifications of a common type. Normally the eye-stalk corresponds to the protopodite of an abdominallimb, consisting of a short basal and a long cylindricalterminal joint, the distal surface of which is covered withcorneal facets. In A. Milne-Edwards Palimirtiswo. finda normal ophthalmite on the right side, but the left one has taken on antenniform Fig. 77.—Cephaloii of a Kock-lobstcr {Palimiruspenicillatus),with an antenniform process growing from the inneraspect of the eye-stalk. (After Howes.) Professor Howes points out that the corneal facetson the eye-stalk of decapod crustaceans do not inmany instances surmount the whole of the free sur-face ; frequently the outer free border is destitute ofcorneal facets, and often is swollen and well differen-tiated. This is so in Palinuriis, and would serve tosupport the view that the facetted portion of the oph- Proc. Zool. Soc. 1889. A TA VISM OR RE VERSION. 141 thalmite was exopoditic, whilst the inner portion, whichfurnished the antenniform process, was endopoditic incharacter. The interest of this specimen lies in the fact that it isexactly analogous to the conversion of an element of aflower, say a stamen, into a leaf Although I have madea wide search, nothing in any way comparable to thisspecimen can be found recorded in zoological literature,but there
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