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



the diaphanous condition of the front part, may likewise be easily explained as subser- 

 vient to sueli a function. 



That the organs in (juestion eannot, as formerly held, be eyes, may lie inferred from 

 several facts : — 1. The nerve that penetrates the organs, or at least those belonging to 

 the trimk, is very thin, and does not give rise to any special (retinal) expansion. 2. The 

 structure of the hinder part of the globule is wholly different from that observed in true 

 eyes, being completely filled with a cellular mass, in the centre of which the fibrous 

 corpuscle lies embedded, and having its pigment-coating not internal liut external. 

 3. The arransement rif the organs belonging to the tail is such, assuming the organs to 

 be eyes, as by no means to admit of a good visual impression, the constant motion of the 

 pleopoda approximating the organs at very short intervals, whereas the effect of phosphor- 

 escence may for that very reason be materially aug-mented, giving to the light a glitter- 

 ing or tremulous lustre. 4. Finally, 1 have found, as stated above, a similar organ 

 embedded in the pedicle of the true eyes themselves, and this organ, being immobile, also 

 entirely lacks the front hemisphere with its lenticular corpuscle, whereas the hinder one 

 in every respect agrees with the posterior part of the other organs, exhibiting in the 

 centre a large bunch of phnspliorescent fibres, and externally a coating of red idgment 

 (see PI. XL fig. 8). It is certainly far from probable that any one examining the last 

 of these organs would venture to assign it the function of sight : and, indeed. Professor 

 Claus, who has recorded and figured the organ in the larvje — in the adult animal it 

 would seem to have totally escaped his attention — has nothing whatever to state respect- 

 ing its probable function. Meanwhile, the organ undoubtedly bears the closest relation to 

 the above described gloljules, both in regard to structure and function, the lisdit it v)ro- 

 duces being, in fact, very intense, though comparatively more steady, than is that from 

 the other movable organs. Since the eye-pedicles, however, are themselves movable, 

 the animal may also, to a certain extent, be able to vary the ett'ect of these organs.' 



Nervous System (sei' PI. XII. fig. :jO). — The nervous cord in the Euphausiidaj exhibits 

 certain rather striking peculiarities as compared with that in other Schizopods. Thus, the 

 number of separate ganglia lielonging to the anterior division of the body is greater than 

 in any other known form of podophthalmous Crustaceans, since, exclusive of the cerebral or 

 supra-cesophageal ganglion, no less than eleven ganglia occur, all of which, however, lie 

 embedded, as it were, within a <-ommon envelope of connective tissue. Tlit.' most anterior 

 oidy of these ganglia, belonging ap}iarently to the mandiliular segment, would seem to 

 present all the features of a simple nervous dilatation, whereas the succeeding ones consist 

 of two well-marked lateral halves, and are connected by doul)le and somewhat distant 

 commissures. Each of the two pairs of maxillaj are innervated l)y their separate ganglion, 

 w^hereas these ganglia in most other Crustacea are, as is well-known, united and consoli- 

 dated with the mandibular ganglion into one nervous mass. The two posterior ganglia 



' Sei- >;air. CliiiU. Exp., vul. i. \i. 743, 18S:>. 



