In the class of the Cirrhipedia a sufficient number of facts is known to ascertain us of the presence of eye spots on the hypostomas of the larva. The researches of SPENCE BATE[43] show in the larva of Balanus balanoides, on the hypostoma or labrum, which he calls proboscis, an eye, a little from the posterior margin of the labrum. It seems during the various moults of the animal to have changed its place, being in the two first moults situated near the anterior margin of the hypostoma. In Clitia Strömi it lies at the anterior part of the labrum (figs. 9, 10). SPENCE BATE does not accept the opinion of their nature as eyes, but the following authors as DARWIN and CLAPARÈDE agree in considering these spots as eyes. DARWIN[44] describes two such eyes in Lepas australis and, if I catch his meaning rightly, one on each side of the labrum. CLAPARÈDE has given a figure of the larva of Lepas anatifera[45] in the hypostoma of which (by him called »Rüssell», proboscis) a single eye is seen, having at the sides two round problematic organs, that he at first considered as auditory cells, but later as eyes. HESSE[46] has also in a species of Scalpellum seen several coloured spots on the inferior surface of the carapace, below the antennæ and he expressly says that they are eyes and a special pair of supplemental eyes that are becoming functional after the first moult. [Footnote 43: On the development of the Cirripedia, Ann. Mag. Nat. list. 1851, p. 324, pl. VI figs. 1, 2, 3, pl. VII fig. 10.] [Footnote 44: Monogr. of Cirripedia I p. 17.] [Footnote 45: Beobachtungen ... über wirbellose Thiere, 1863, pl. XVII fig. 22.] [Footnote 46: Mémoire sur les métamorphoses que subissent les Anatifes appelés Scalpels obliques. Annales des Sciences nat. 1859. Tome XI p. 163.] These sternal eyes in the larva are previous to the eyes in the dorsal side of the later stages and whenever such are discovered in other groups of adult animals as the trilobites they must of course be considered as remnants from the larval stage. As a rule, in several tribes of the crustacea it has been observed that the eyes originate on the ventral or sternal side of the body and in the advancement of growth move to the superior side. So according to PACKARD and others the embryo of Limulus has originally the median eyes on the ventral side. In the same way the cephalic eyes of Dalmanites move, as BARRANDE has shown, from the ventral side to their permanent place on the superior side of the head shield. But while in the Cirrhipedia the larval or hypostomic eyes are lost in the adult they remain on the hypostoma of a great number of the adult trilobites and have probably left their mark behind in A pus. No wonder then that we find these maculæ developed as precursors of the hypostomic eyes in a number of the oldest and in other respects blind trilobites as the Olenellidæ and Paradoxidæ to which they may have been of some use as a sort of visual organs, though probably very imperfect.