32 DISCOVERY REPORTS 



In the antennule the peduncle consists of three segments, of which the basal is pro- 

 longed externally into a strong spine, extending to, or a little way beyond, the distal 

 margin of the distal peduncular segment (Fig. 6 c). The flagella are not greatly altered 

 from the form found in the 2nd Calyptopis ; the outer flagellum bears two sensory fila- 

 ments terminally. The antenna, mandible, ist and 2nd maxilla and the ist thoracic ap- 

 pendage (Figs. ()f,g, h) are unchanged. 



Behind the ist thoracic appendages are five pairs of bilobed "sausage-shaped" 

 thoracic rudiments (Fig. 6^). In each limb the endopod is longer than the exopod. The 

 posterior limbs are shorter than the anterior ; there is no trace of segmentation or setae 

 on the limbs. In Fig. 6 // the ist thoracic limb has been shown along with the succeeding 

 five limbs to compare the difference in size. 



The luminous organ at the base of the eye, recognizable as a bunch of fibres, is the 

 only one that can as yet be distinguished. 



SUMMARY OF PREVIOUS KNOWLEDGE RELATING 

 TO THE FURCILIA AND CYRTOPIA STAGES 



In the report on the Schizopoda collected by H.M.S. ' Challenger' (Sars, 1885), in the 

 section dealing with development of Euphausiidae, it is stated that the three schizo- 

 podous genera, Calyptopis, Furcilia and Cyrtopia of Dana were proved by Claus (1863) 

 to be different stages in the development of Euphausiidae. Metschnikoff (1869, 1871) 

 describes still earlier stages, which Sars in accordance with earlier authors designates 

 the Nauplius and Metanauplius stages. For the three succeeding stages Sars applies the 

 generic denominations suggested by Dana. It is the last two of these stages, namely 

 Furcilia and Cyrtopia, which are to be discussed here. They are described by Sars as 

 follows : 



Furcilia stage. Compound eyes more fully developed (than in Calyptopis), mobile, and projecting 

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

 pairs of legs and pleopoda successively developing. 



Cyrtopia stage. Antennular flagella becoming elongate and distinctly articulate. Antennae trans- 

 formed so as not to serve the purpose of locomotion. Posterior legs and gills successively appearing. 



Within the division which he terms Furcilia, Sars in his description of Euphausia 

 pelhicida, Dana (= E. superba), recognizes three stages which he names respectively first, 

 intermediate and last Furcilia. Similarly in the Cyrtopia of this species he recognizes 

 two stages, a first and last. The distinction between different stages of both Furcilia and 

 Cyrtopia is based mainly on the degree of development of the appendages. 



Referring to the development of Thysanopoda tricuspidata Sars states (p. 167) that 

 there are several successive stages of Furcilia in the collection. He only refers to one 

 Cyrtopia stage. In Nematoscelis rostrata, G. O. Sars, he recognizes two Furcilia stages 

 and one Cyrtopia. 



Brook and Hoyle (1888), describing the metamorphosis of British Euphausiidae, state 

 that in the Furcilia of one species there are eleven moults judging from the comparative 

 development of the pleopods, thus : 



