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



limbs oiilv present, the anterior (antennulse) simple, the two others (antennae and 

 mandibular legs) biramous, natatory. 



2. Metanauplms Stage. — Form of body as in the Nauplius stage. Two pairs of 

 limbs (anteunul£B and antennae) only developed; mandibular legs lost. Mandibles, 

 maxillfe, and maxillipeds present merely as bud-like prominences. 



3. Calyptopis Stage. — Body divided into its two principal divisions. Carapace 

 distinct, forming anteriorly a hood-like expansion. Tad becoming segmented. Com- 

 pound eyes still imperfectly developed, immobile, and covered over by the carapace. 

 Mandibles, maxillfe, and maxUlipeds distinct, but no trace of legs or pleopoda. Uropoda 

 becoming developed. 



4. Furcilia Stage. — Compound eyes more fuUy developed, mobile, and projecting 

 beyond the sides of the carapace. Antennae still retaining their original structure, 

 natatory. Anterior pairs of legs and pleopoda successively developing. 



5. Cyrtopia Stage. — Antennular flagella becoming elongate and distinctly articulate. 

 Antennae transformed, so as not to serve the purpose of locomotion. Posterior legs and 

 gUls successively appearing. 



6. Post-Larval Stage. — iVll the legs developed. Telson assuming its definitive form 

 and armature. 



The difficulty attending an accurate reference of the numerous larval forms contained 

 in the Challenger surface gatherings to the several species described above has been very 

 great. However, by carefully examining all the forms, and comparing one with the 

 other, I have nevertheless been enabled to trace out the development, more or less 

 completely, in four different species belonging to as many genera. In the following 

 pages I purpose describing the several stages of each sj)ecies in detail. 



Early Larval Stages of Nyctiphanes australis, G. 0. Sars (PL XXVIIL). 



The larvae treated of here I have felt warranted in referring to the above-named species, 

 taken, as they were, from precisely the same bottles as the adult specimens of this form, 

 and from localities where no other Euphausiidae were obtained. Moreover, as stated above, 

 two of the adult females were ovigerous, whence it may be inferred that hatching time 

 was about to commence. From this cause, apparently, no older larval stages than those 

 here described were found in the jars. 



Metanauplius Stage (figs. 1-3). — This is the earliest stage known to the author, and 

 that, it would seem, immediately succeeding the true Nauplius stage. It was represented 

 by a solitary specimen, which measured only -g mm. in length. 



The body is oval in form and does not exhibit the slightest trace of segmentation, nor 

 any distinct limitation of the two principal di\asions, so well defined in the adult animal. 



The carapace is, however, distinctly indicated even at this early stage, forming, as it 



