A STUDY IN MORPHOLOGY. 
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antenna, without its hairs. There are no cutting blades or hooks upon the basal 
joints of either pair of antennae or the mandibles. 
The labrum (L) is somewhat larger and more prominent than it was at the stage 
before, and the anus is still absent. 
The second free Nauplius stage or m eta- Nauplius. 
In about twelve or fourteen hours the Nauplius sheds its skin and assumes the 
form shown in Plate 3, fig. 26. From the prominence of the region of the hind body, 
and the presence of a carapace, Claus has distinguished this stage of development, in 
allied forms, by the name of meta -Nauplius. 
I did not actually witness the change, and am not sure of the exact length of the 
first free Nauplius stage, but it is not more than eighteen, and probably no more than 
twelve hours long. A Nauplius which had hatched from the egg some time during 
the latter part of Monday night was placed, alone, in a watch-glass of sea-water, and 
changed into the one from which fig. 26 was drawn before 9 p.m. on Tuesday evening. 
The differences between this and the preceding stage are sufficiently great to 
attract the attention at first sight. The length, as measured from the ocellus to the 
posterior end of the body, has increased from ywqq inch to -poo u inch. The labrum ( L) 
is longer and more prominent. The first antennae (A) are unjointed, and the joints of 
the second antennae (An) and mandibles (. M ) are almost absent. 
The hairs at the tips of the endopodites of the second antennae and mandibles (en) 
are irregularly plumose, and a long slender slightly curved hair is carried by each of 
the larger joints of the endopodite of the second antennae. 
On the inner posterior edge of the basal joint of the mandible, a short stout curved 
hook or blade has made its appearance. The four pairs of buds on the ventral surface, 
posterior to the labrum, are in the same condition as before, but the telson (T) is quite 
prominent, notched or forked, and furnished with two pairs of short stout spines, the 
inner pair being much longer than the outer. A well-marked fold (c) of the surface 
of the body now marks the posterior and the lateral edges of the carapace, but this 
line is not continued on to the anterior end of the body, and the posterior edge is not 
yet raised or separated from the hind body as it is, according to Metschinukoff, in 
the last Nauplius stage of Euphausia. 
The pigment-spots (p) are drawn out in such a way as to surround a large rectan¬ 
gular area, at the posterior end of the carapace, and in the region where the heart 
is placed at the next stage. 
The digestive tract is now visible in a side view. The oesophagus (os) runs upwards 
and forwards from the mouth, situated under the overhanging tip of the labrum, and 
then bends backwards and upwards to open into the floor of the stomach (s) ; the side 
walls and top of the stomach could be made out without difficulty, but I was not able 
to decide whether its ventral wall is complete or not. It is divided by a fold or flap 
L 2 
