116. Mouth Parts of the Louse.
117. Mouth Parts of Louse.
118. Mouth Parts of Louse.
After the egg has been fertilized by the male, the blastoderm, or primitive skin, forms, and subsequently two layers, or embryonal membranes, appear; the outer is called the amnion (Fig. 114, am), while the inner visceral membrane (db) partially wraps the rude form of the embryo in its folds. The head (vk) of the embryo is now directed towards the end of the egg on which the hairs are situated; afterwards the embryo revolves on its axis and the head lies next to the opposite end of the egg. Eight tubercles bud out from the under side of the head, of which the foremost and longest are the antennæ (as), those succeeding are the mandibles, maxillæ, and second maxillæ, or labium. Behind them arise six long, slender tubercles forming the legs, and the primitive streak rudely marks the lower wall of the thorax and abdomen not yet formed. Figure 115 represents the head and mouth parts of the embryo of the same louse; vk is the forehead, or clypeus; ant, the antennæ; mad, the mandibles; max1, the first pair of maxillæ, and max2, the second pair of maxillæ, or labium. Figure 116 represents the mouth parts of the same insect a little farther advanced, with the jaws and labium elongated and closely folded together. Figure 117 represents the same still farther advanced; the mandibles (mad) are sharp, and resemble the jaws of the Mallophaga; and the maxillæ (max^1) and labium (max^2) are still large, while afterwards the labium becomes nearly obsolete. Figure 118 represents a front view of the mouth parts of a bird louse, Goniodes; lb, is the upper lip, or labrum, lying under the clypeus; mad, the mandibles; max, the maxillæ; l, the lyre-formed piece; and pl, the "plate."
119. Louse of Cow.
