In the primitive trilobite Harpes the ocelli remain functional through life and no compound eyes are developed; we may infer that the early appearance and strong development of the ocelli in the larvae of both Limulus and the scorpion are, in view of their retention in later life, with diminished force, rather suggestive of their having been the first eyes of the ancestral forms.
As the swimming legs are clearly a secondary acquirement their larger size and probably that of the other legs also, is a purely larval feature in
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| Figure 24 | Dorsal and ventral views of last larval stage of Limulus before the appearance of the telson. l, liver tubule; I, chelicera; op, operculum. (From Kingsley) |
line with the greater size of the lateral eyes, both of these being coenogenetic larval characters developed in connection with the greater agility of the larva. The larvae of Limulus [see text fig. 24] possess relatively longer legs than the adults, and this is especially notable in the last pair that projects considerably beyond the carapace. A still better analogy is found in the lively megalops stage of the crab [see text fig. 23] where immense eyes and long legs are correlated features.
