REPORT ON THE CRUSTACEA MACRURA. 231 



The Development of Perueus is only approximately known. Fritz Miiller's statement 1 

 that the brephalos is a Nauplius has been fully accepted by some and cautiously received 

 by others, and the recent researches of Professor Brooks on the genus Leucifer have 

 strengthened the belief that the brephalos of Pcnasus may be in the Nauplius form 

 also. 



The observations made on the development of other forms of Macmrous Crustacea have 

 shown that many closely associated species produce their young in very distinct stages 

 of development. Thus the brephalos of Crangon vulgaris differs largely from that of 

 Crangon arcticus, the former being in the Zoea, and the latter in the Megalopa stage, and 

 that of Homaralphaeus differs in the same degree from that of Alpheeus, and yet the 

 parents cannot be distinguished from each other. 



Fritz Midler described a Nauplius which he found in the open sea, and supposed to be 

 the young of Penams. 2 It is destitute of distinct somites, pyriform in shape, rounded 

 in front, - 4 mm. in length, and - 2 mm. in breadth at the widest part, which is just 

 behind the head, and gradually narrowing posteriorly untd at its caudal extremity 

 the breadth is just one-fifth of the length of the animal, and it terminates on each 

 side in one long and one short spine. In the centre of the anterior margin is a small, 

 black, clearly defined ocellus. To the ventral surface are attached three pairs of 

 appendages. The first is single-branched, furnished with a few simple hairs, and 

 situated close to the frontal margin ; the second is immediately behind the first, it is 

 biramose, and has both its branches furnished with ciliated hairs. These two pairs of 

 appendages are nearly as long as the animal, but the third pair is only half that length, 

 and like the second it is biramose and furnished w T ith ciliated hairs on each 

 branch. 



The animal at this stage is rather opaque and of a brownish colour, darkest towards 

 the extremities of the appendages. It is by these little appendages that the young 

 creature swims, lashing the water, as Fritz Midler says, like a man swimming per- 

 pendicularly with outstretched arms, and having slender willow branches in his 

 hands. 



In the next developmental stage the animal is 0*5 mm. in length. The colour and 

 appendages are the same, but the posterior extremity of the animal is prolonged into two 

 thick processes, at the apices of which there still exist the two long spines as in the 

 previous stage ; to these several less prominent ones have been added. The number 

 of hairs attached to the anterior appendages has increased also. At this stage the first 

 indication of the carapace is seen in the presence of a transverse line across the dorsal 

 surface of the animal. 



1 Fritz Mliller, Die Verwandlung der Garneelen, Erster Beitrag., pp. 8-23, Taf. xi., 1863 ; Archiv f. Naturgesch., 

 Jahrg. xxix. Bd. i. pp. 8-23, 1863 ; Ann. and Mag. Nat. Hist., vol. xiv. p. 104, 1864. 



2 Fritz Mliller, he. cit., p. 9, pi. xi. fig, 1. 



