SCHIZOPODA AND CUMACEA 



its last pair of legs much less so than in the last-named form. This shows that there is 

 considérable différence between the development in thèse two species of the same genus. 



In his standard work on the Euphausiacea of the Challenger, G. O. Sars fills two 

 plates (pi. XXIX and XXX) with figures illustrating the development of his Euphausia pellucida, 

 and the description of the larval stages occupy nearly nine pages. He thinks that the deve- 

 lopment of the members of this order (which he regards as a family) is so uniform that he 

 gives short diagnoses « of each of the principal stages peculiar to the development of the 

 Euphausiida: » ; thèse stages he names Nanplius stage, Metanauplius stage, Calyptopis stage, 

 Fui alui stage, Cyrtopia stage and Post-larval stage; it may be added that in the description 

 of E. pellitcida he has three subdivisions of the Furcilia stage and two of the Calvplopis stage. 

 And let us now take two examples for comparison between a couple of his stages and animais 

 from the Belgica. 



In the diagnosis of the Furcilia stage we find (p. i5o) : « Anterior pairs of legs and 

 pleopoda successively developing », and in his description of the last Furcilia stage of 

 E. pclluada (p. idj) : « In this stage ail the pleopoda hâve become developed, and act in 

 the living animal as true swimming organs. On the trunk the second pair of legs hâve become 

 articulated, though they are still much smaller than the first, and behind it a few minute 

 bud-like projections may be seen, apparently representing two additional pairs of legs, besides 

 the first trace of the gills. » On pi. XXX, fig. 3 and fig. 40 represent respectively the antennula 

 and the telson (and uropod) of the last Furcilia stage, and thèse figures agrée completely 

 with the shape of the same organs in stage C of E. superba. But in the last Furcilia stage 

 even the second pair of legs are still small and the following pairs only bud-like, while in 

 stage C of E. superba ail five pairs of legs look essentially as in the adults, those of the fifth 

 pair being so long that their end is situated vertically below the posterior half of the eyes. 

 Consequently thèse larva? of the two species differ from each other in such an important 

 point as the development of the legs, while they agrée in most other features. 



In the description of his first Cyrtopia stage of E. pellitcida Sars says (p. i57-i58). « The 

 character distinguishing most prominently this stage from those preceding it, is the total 



change in structure and function of the antennas Of the two branches, the one has assumed 



the character of the scale, the other of the flagellum. » According to this description and 

 his fig. 8 on pi. XXIX and fig. 7 on pi. XXX his larva agrées in this respect with stage A of 

 my Euphausia sp., but further comparison shows that in my larva the trunk-legs are considerably 

 more, the telson much less developed than in Sars' animal, as seen on his fig. 8 on pi. XXIX 

 and fig. 41 on pi. XXX. 



The features pointed out show that there is much différence between the development 

 of the three species of the same genus : when a set of organs are similarly developed in 

 larvae of two species, other organs are either considerably more or much less developed in 

 one of thèse larvae than in the other. Therefore it may be difficult to refer several larval 

 forms to the Furcilia or Cyrtopia stages as they are defined by Sars. But our knowledge 

 of the development of the species of this order is still in its infancy. 



