A NAUPLIUS LARVA 59 
CRUSTACEA 
A LARVAL ENTOMOSTRACAN. A NAUPLIUS LARVA 
In an aquarium containing copepods or ostracods there are 
sure to be numbers of the young larve of these animals. They 
are minute, free-swimming forms and are called nauplii, and may 
be recognized by the triangular or oval, unsegmented body, 
which bears three pairs of appendages and a median eye. 
Nauplii of marine entomostracans may also be met with in 
large numbers among the small animals obtained by skimming 
the surface waters of the sea with a fine net. 
Examine in a watch-glass under a microscope water contain- 
ing sediment taken from a jar in which are copepods or ostra- 
cods. Find a nauplius; the ostracod nauplius differs from that 
of the copepod by being enclosed in the characteristic bivalve 
ostracod shell. If marine plankton is at hand, look for several 
kinds of nauplii in it. 
Study the structure of a nauplius. Observe the unseg- 
mented body; if the animal is not newly born, signs of segmen- 
tation may have begun to appear. Observe the three pairs 
of segmented appendages ; the segmentation, however, is often 
indistinct. These appendages are homologous to the first and 
second pair of antenne and the pair of mandibles of the adult 
animal. As in the adult, the first pair is uniramous; the 
second and third pairs are biramous. Both of the latter two 
pairs are used for locomotion, although it is probable that they 
also act as jaws. The median eye will be seen, and the straight 
digestive canal. 
Exercise 1. Draw a nauplius on a large scale and label all the 
parts above mentioned. 
