. A text-book of invertebrate morphology. Invertebrates. 418 INVERTEBRATE MOBPHOLOOT. antennules are uniramous and, like the other limbs, but indis- tinctly jointed, the antennules and mandibles being, however, biramous and possessing strong setse at their bases which function as jaws, though both pairs of appendages are essen- tially locomotor. Judging from the appendages, therefore, the Nauplius may be regarded as consisting of five segments, one corresponding to the prostomial lobe of Annelids and contain- ing the primitive cerebral ganglion (archicerebrum), one cor-. FiG. 191.—NAiTPLrDB OF
. A text-book of invertebrate morphology. Invertebrates. 418 INVERTEBRATE MOBPHOLOOT. antennules are uniramous and, like the other limbs, but indis- tinctly jointed, the antennules and mandibles being, however, biramous and possessing strong setse at their bases which function as jaws, though both pairs of appendages are essen- tially locomotor. Judging from the appendages, therefore, the Nauplius may be regarded as consisting of five segments, one corresponding to the prostomial lobe of Annelids and contain- ing the primitive cerebral ganglion (archicerebrum), one cor-. FiG. 191.—NAiTPLrDB OF OetocliUus sepientrionalis (after Gbobbkn). responding to each pair of appendages and one to the region of the body behind the mandibles. A Nauplius of this simple form may be regarded as typical and is that which is found in the majority of the Copepoda and in the Cirrhipedia as well as in some Branchiopoda [^stheria, Limnadia). In the Ostracoda the arrangement of the limbs and segments is the same, but the bivalved shell characteristic of the adult is already developed, giving the Nauplius an ap- pearance very different from that of the Copepoda. Not un- frequently, however, as for instance in Apvs among the Branchiopoda, and Leptodora among the Cladocera (the re- maining Cladocera, so far as is known, leave the egg with the adult form), the Nauplius, though possessing only the three pairs of appendages, yet shows indications in the post-mandib- ular region of a varying member of additional segments, and to this form it is convenient to apply the name Metanauplius. As a rule in the Eutomostraca further development con- sists of a series of moults (ecdyses), an increase in the number of segments and appendages and modifications of the latter taking place at each ecdysis, until the adult form is attained. No special larval forms beyond the Nauplius are common to. Please note that these images are extracted from scanned page images that may have been digitally enhanced for re
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