vl LABRUM AND MACULAE 233 
the doublure is not separated from the lateral parts, or from the 
dorsal part of the cephalic shield. 
The “labrum” or “hypostome” is attached to the doublure in 
front (Fig. 137, B, a); it is commonly an oval or shield-shaped 
plate, but is occasionally nearly square. Its surface is sometimes 
divided into two or three areas by shallow transverse grooves 
(Fig. 141, A). Just behind the middle of the hypostome, or 
when transverse grooves are present either in or near the anterior 
groove, there are often found a pair of small patches or “ maculae ” 
which are more or less oval or elliptical in outlne (Fig. 141). 
The maculae may be (1) surrounded by a raised border, or (2) in 
the form of pits, or (3) raised like tubercles. In some cases the 
Fic. 141.—A, Hypostome of Bronteus polyactin, Ang. showing maculae, x 4. B, Left 
macula of Bronteus irradians, Lindst. x 12. (After Lindstrom. ) 
entire surface of a macula is smooth and glossy; in others either 
the whole or a part is covered with granules, and in the latter case 
the granules may be limited to the internal third (Fig. 141, B) or to 
the central portion. Sections of a macula show that the granules 
are really globular lenses similar to those of the compound eyes 
on the dorsal surface of the head. Some of the maculae which 
are without lenses show no structure, but in others there is a 
spongy or irregularly polyhedric structure with prisms, resembling 
the marginal zone of the prismatic eyes of some genera. There 
seems no doubt that the maculae with lenses are visual organs, 
and those without are degenerate eyes. They occur in some 
genera which, according to Lindstrém, are without eyes on the 
dorsal surface. Maculae do not appear to be present in other 
Crustacea, but they have been compared with a median organ, 
found just in front of the hypostome in Branchipus.' Maculae 
1 Spencer, Geol. Mag. 1903, p. 489. 
