REPORT ON THE CRUSTACEA MACRURA. 



451 



The digestive tract has become visible ; the oesophagus, which commences imme- 

 diately behind the labium, rising upwards and backwards to open into the floor of 

 the stomach. The intestine is small, with thin walls, and it follows the dorsal 

 curvature of the body to the anus, which is placed just in front of the spines of the telson. 



The nervous system is present in the form of a cerebral ganglion and a neural mass 

 that is obscurely divided into segments, which passes beneath the stomach. 



Within twelve hours the animal moults, and increases from j^ra (0"225 mm.) to xow 

 (0'5 mm.) of an inch, or to rather more than twice its length, and changes its form from 

 that of a Nauplius to that of a Zoea — a change chiefly due to the development of the 

 carapace and the great increase in the length of the pleon. 



The great increase in size, more than twice, and the remarkable variation in form are 

 such, that nothing less than the exactitude shown in the observations made by Professor 

 Brooks would have precluded critical discussion, but he, 

 having placed the Nauplius which has just been described, 

 alone in a watch-glass of sea-water, at 9 p.m. on September 

 28, found on the 29th at 9 a.m. that it had changed into 

 the Zoea form. 



This Zoea has the carapace developed in a horse-shoe 

 form, much like that of the king-crab, Limulus, and it 

 forms about one-half of the entire length of the animal. 

 The frontal margin is produced anteriorly in the median 

 line to a strong and pointed rostrum, about one-third of 

 the length of the carapace. The posterior margin is con- 

 cave and produced in the median line into a short tooth 

 that is oblicmely elevated, and the postero-lateral angles 

 are produced to long, posteriorly directed teeth. The 

 walls^ of the carapace are folded down, and laterally com- 

 pressed, so that all the appendages except the antennae 

 are almost completely enclosed and protected. 



Dana 1 described and figured two specimens of this 

 form under the name of Erichthina demissa ; the earliest 

 stage had no eyes visible, only the central ocellus, but in the older one the eye was 

 present in a more advanced stage than that shown in either of Brooks' figures. 



This is as far as Professor Brooks was able to trace the development of one specimen, 

 but he has shown from others taken at a similar period that there are three forms that 

 correspond with this Zoea moult. 



This stage corresponds with the accompanying figure (fig. 54), taken from Willemoes 

 Suhm's drawings, which he defines, as — 



1 U.S. Explor. Exped. Crust., p. 634, pi. xlii. figs. Za-d. 



Fio. 54. — Zoea of Lucifer reynmulii. gl, 

 gland in the carapace ; Pl,s, provisional 

 segments of the pleon ; la, labrum ; mdb, 

 mandible ; mx l , first maxilla ; mx", second 

 maxilla ; mxp, maxilliped ; g 1 , gnathopod. 



