322 BULLETIN OF THE 



that a detailed description of them would be superfluous. In specimens 

 8 mm. or 9 mm. long the transverse suture of the exopod of the swim- 

 merets (Fig. 15, XIX, re) has not yet appeared. As in full-grown 

 individuals, the inner side of the tip of the styliform appendage of the 

 preceding abdominal members (Fig. 26, s) is furnished with microscopic 

 curled hairs (Fig. 27), whose function I cannot imagine. They occur in 

 both sexes. The internal branch of the second pair of abdominal mem- 

 bers in mature male specimens presents a second slender inner append- 

 age (Fig. 28, s') fringed with hairs on its outer margin. The small 

 eudopod of the first pair of abdominal appendages, moreover, is differ- 

 ently shaped in the two sexes. In the male, the distal third widens and 

 trends slightly inward ; on the inner margin, near the base, are some 

 long setse ; the distal portion bears short, plumous seta?. In the female, 

 the endopod narrows gradually from its root to the tip, and is fringed 

 at the end and along the internal border by long feather-like hairs. 



In the above-described series of larval forms I have never obtained 

 the third stage directly from the second, but with this exception I have 

 actually reared in confinement each successive stage from its predecessor, 

 from the first to the sixth inclusive. 



The only larva known to me on this coast liable to be confounded 

 with Palcemonetes is that of Virbius zostericola Smith. In specimens 

 6.5 mm. long, still in the Schizopod condition, the carpus of the second 

 pair of feet is already tri-articulate, and the setse of the telson, form of 

 the antennal scale, and other characters serve to distinguish it from the 

 young Palcemonetes. 



It appears, from what precedes, that Palcemonetes issues from the 

 egg in the zoea-form, i. e. provided with a pair of compound eyes, 

 two pairs of antenna), two pairs of maxilla), and three pairs of swim- 

 ming-feet, the future maxillipeds. Behind the third pair of swim- 

 ming-feet are the rudiments of the following two pairs of append- 

 ages in the shape of double sac-like structures. No gills exist, the 

 aeration of the blood being accomplished through the general integu- 

 ment, and especially under the sides of the carapace, by means of a cur- 

 rent of water maintained, as in the gill-bearing adult, by the constant 

 motion of the broad external plate of the second maxilla?. The abdomen 

 is wholly devoid of appendages, and the telson is not clearly marked 

 off from the sixth abdominal segment. 



As development proceeds, the rest of the thoracic legs are unfolded in 

 succession from before backward. The only break in the regular order 

 of succession is caused by the unfolding of the last pair earlier than the 



