. Elementary text-book of zoology. Zoology. CIKEIPEDIA. 443 In in oTiiatuni and I hi a Cuminyii; also with the remarkable genera Cryptophialus and Alcippe (tig. 350). The males of these forms are not only small and dwarfed, but also, according to Darwin, have neither mouth, digestive canal, nor thoracic appendages. As a rule, two or sometimes more attach themselves to the body of the female. Development.—The eggs, while still within the brood-pouch, undergo an irregular segmentation. The clear cells arrange them-, selves around the food yolk in the form of a blastoderm, the ventral side of whi
. Elementary text-book of zoology. Zoology. CIKEIPEDIA. 443 In in oTiiatuni and I hi a Cuminyii; also with the remarkable genera Cryptophialus and Alcippe (tig. 350). The males of these forms are not only small and dwarfed, but also, according to Darwin, have neither mouth, digestive canal, nor thoracic appendages. As a rule, two or sometimes more attach themselves to the body of the female. Development.—The eggs, while still within the brood-pouch, undergo an irregular segmentation. The clear cells arrange them-, selves around the food yolk in the form of a blastoderm, the ventral side of which soon becomes considerably thickened in consequence of the appearance of the mesodermic layer. The larvje leave the egg as Nauplii (tig. 351, a, b), of oval or pear-shaped form, with unpaired frontal eye, lateral frontal horns, and three pairs of appendages, of which the anterior is simple, the two next biramous and closely beset with swimming setfe. After several moults, the larva, Avhich has grown to a considerable size, enters on a new stage of de- velopment, the so-called Cypris stage (pupa) (fig. 352). The reduplica- ture of the skin has the form of a bivalve mussel-like shell, through the gaping ventral edges of which the appendages can .be protruded. While the form of the shell recalls that of the Ostracoda, the structure of the body, so far as the segmenta- tion and form of the appendages are concerned, approximates to that of the Copepoda. The anterior ap- pendage of the Nauplius larva has given rise to a four-jointed antenna, the penultimate joint of which has become large and disc-shaped and contains the opening of the cement gland, while the terminal joint bears in addition to tactile set« one or two delicate lancet-shaped olfactory hairs. The frontal horns are transformed into two conical prominences near the an- terior margin. Of the two pairs of biramous appendages, those which correspond to the second pair of antenna- are cast off, while. FIG. 352.—Median
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1884
