A STUDY TN MORPHOLOGY. 75 



antenna, without its hairs. There are no cutting blades or hooks upon the basal 

 joints of either pair of antennte 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 ??u-?a-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, GLAUS has distinguished this stage of development, in 

 allied forms, by the name of meia,- Nauplius. 



I did not actually witness the change, and am not sure of the exact length of the 

 first free Nauplius stage, bnt 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 y-jjol) hich to J-Q-Q-Q 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 antenna? 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 METSCHINCKOFF, in 

 the last Nauplius stage of Eupliausia. 



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 (a?) 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 



