262 DISCOVERY REPORTS 



In the species described in this paper and in Eitphausia stiperba, E. krohnii, Thysanoessa 

 macnira, T. raschii and Meganyctiphanes norvegica, the number of terminal spines on the 

 telson does not begin to be reduced until, or until after, all the pleopods become setose. 

 But this is not invariably so in euphausians : in Thysanopoda aeqiialis and in Nematoscelis 

 microps the development of the pleopods is accompanied by a reduction in the number 

 of terminal spines from the original seven (Lebour, 1926 c, pp. 770, 768). Lebour's 

 descriptions of the larvae of these two species interpreted in terms of Furcilia stages as 

 used in this paper are tabulated below. 



Table III 



* Lebour {ibid., p. 768) writes: "In the second Furcilia (stage I above). . .there are seven giving rise to 

 five.. . .This may, however, be abnormal, for in the sixth Furcilia (stage II). . .there are specimens with 

 seven spines giving rise to three.. . ." I presume there were also specimens with five terminal spines. 



It would be interesting to know the state of development of all the appendages of the 

 stage with one terminal spine and three pairs of postero-lateral spines in the two species 

 (stage V of Thysanopoda aequalis and stage IV of Nematoscelis microps). The thoracic 

 limbs and the gills of this stage of the five species of Eiiphaiisia whose development is 

 described in this paper are at roughly the same point as one another in development. 

 It may be that the whole development is speeded up in Thysanopoda aequalis and 

 Nematoscelis microps ; that not only is the telson modified earlier than in other species 

 but that the appendages develop earlier too. 



It has already been shown that in a number of euphausiids the comparative develop- 

 ment of the Furcilia is roughly the same : first the pleopods successively appear, and 

 then the telson becomes modified ;i but that at the same time the steps along the first 

 part of the path of development might be different in different species. It now appears 

 possible that in other euphausians the comparative development may be very different. 



1 At the same time, in the five Euphausia described here, the thoracic appendages develop in each at 

 roughly the same rate. 



