ABSTRACT
Scope.—In the essay entitled “Limulus an Arachnid,” published in this Journal in 1881, it has been pointed out by one of us (Prof. Lankester) that, amongst other very numerous agreements of structure exhibited by the Scorpions on the one hand and the King Crab on the other, there is a close superficial coincidence in the disposition and the character of the eyes; in both we find a.single pair of simple central eyes, and a lateral or marginal pair of “grouped “or aggregated eyes—the multicorneal lens of the King Crab’s lateral eye corresponding to the numerous (two to seven) small lenses placed in groups laterally on the Scorpion’s head.
‘Sehorganen der Arthropoden,’ Gottingen, 1879.
‘Archiv. f. Mikrosk. Anatomie,’ vol. xvii, 1880.
‘Archiv f. Mikrosk. Anat.’ vol. xvii, 1880, p. 58.
It is important to note the following difference between the lateral eyelet of a Scorpion and a single element of the King Crab’s lateral eye—in the former the ommateum contains more than one retinula, it is retinulate, in the latter it contains but one group of nerve-end cells, truly a retinula when the whole eye-group is considered but in itself non-retinulate. Thus the eyelet of the Scorpion is morphologically more (a larger segment of the original ocular area) than the lens-cone element or eyelet of Limulus.
