232 THE VOYAGE OF H.M.S. CHALLENGER. 



After this stage the link is missing and the chain is again taken up when the young 

 creature has doubled its previous length. Ten or eleven new somites are now found 

 defined, with a pair of appendages attached to the first, the rudiments of others to the 

 five succeeding, and with the posterior pair of pleopoda. It is now in the Zoea condition. 

 From this period the animal can apparently be traced through the several forms that are 

 figured in this Eeport to that of the adult condition. 



On PL XL VIII. fig. 1 is that of a specimen taken and labelled "Sergestes I., young, 

 off New Guinea." 



Length, 4 mm. (0 - 16 in.). 



It was mounted and initialled by Suhm as if for especial reference. The rostrum 

 exists as a small point, and the carapace covers the whole of the pereion. The 

 pleon has the five anterior somites subequal and unarmed ; the third somite is 

 rather longer than the others, and dorsally slightly arched longitudinally ; the sixth 

 somite is nearly as long as the five preceding. The dorsal and ventral margins are 

 parallel, and the telson is bifurcate, each branch terminating in two naked hairs or long 

 spinules. 



The ophthalmopoda are pyriform and well developed. 



The first pair of antennae has a peduncle of three joints, of which the first is longest, 

 and broad at the base, but the otocyst is not yet visible, and the third supports two 

 uniarticulate branches. 



The second pair of antennae has a peduncle that supports a scaphocerite, which 

 increases slightly in breadth towards the distal extremity, where it is armed on the outer 

 side with a small tooth, and fringed on the inner and distal margins with a row of fine 

 hairs. 



The mandibles are well formed but do not carry a synaphipod. 



The two succeeding pairs of oral appendages are not definable in the mounted 

 specimen, but the gnathopoda and the three following pairs of pereiopoda are, the 

 two posterior pairs being as yet in an immature or bud-like condition. The pleopoda 

 are present in an early stage, in a budding condition, except the ultimate pair, which 

 has increased so as to equal in length the bifurcate telson. 



I now pass to the consideration of a series of observations made by Dr. v. Willemoes- 

 Suhm on the development of what he held to be Sergestes tenuis, of which the earliest 

 stage is shown in figure 43; but a comparison of the figure with those of Fritz 

 Muller and Claus induces me to believe that Willemoes-Suhm is mistaken in attri- 

 buting it to Sergestes instead of to Penseus. I give, however, his own notes with each 

 figure. 



