152 "TE1!I!A NOVA" EXPEDITION. 



(lifticult to assipn any reason for tlio stalked eyes of some early larvae (Stouiiatidae, 

 especiallv Sf_i/lt)j)/tt/iri/i/tus). unless it lie mnceded that they may eual)le the larva to 

 see in all directions and help it to maintain a lialance, and, as it is so small and not yet 

 an active swimmer, are not likely \<> \>r injnivd ,,y to impede its progress. 



Defence. — 3l:in\ |)claL;i<- larvae have the iioaes of the head, and especially the 

 praeoperculuni. aimed witli stron.ii; spines, no douht defensive. This is well exemplitieil 

 l)y Thyrsitrs (p. 144, PI. VIII, tigs. 1-3), PI<if>/o'/>hnliis (p. 14fi, PI. X, fig. 4) and 

 Anci/lopxetta (p. 146. PI. IX. figs. 3. 4). The precocious development, prohalily for 

 defensive jmrpo.ses, of the spinous dorsal and pelvic tins in Tlii/isttis has already l>een 

 I'eferred rn. 



5. SYSTEMATIC IMPORTANCE OF LARN'AL CHARACTERS. 



Except in a few groups, of wliii-h the Apodes are the most notalile example, there 

 are no features that characterize pelagic- laival tislies as belonging to one order or 

 anotlier. and it is not eas\- to determine their systematic po.sition unless they are 

 sutticientlv adxaiiced towards the structure of the adult fisli. In all cases the nund)er 

 of mvotomes and nf tin-ravs. if these be developed, are of the greatest help : with these 

 as a ouid(' mic nia\. bv a patient process of trials and eliminations, determine 

 specificallv .some nmst puzzling examples, as. for instance, the post-larval (Jila.r 

 halteaftis; descrilied and figured above (p. 14:-). I'l. \ III. lig. 4). Although it does not 

 appear that the diagnostic characters of the dittcreni orders are likely to lie strongly 

 reinforced li\- larval features, yet the study of a series of larval and young fishes, such 

 as those ccdlected li\' the "Terra Nova,'' confirms and in no degree modifies ideas as to 

 the relationship of the Teleostean orders ami families deriveil from the study of the 

 morphology of the adult tisli. 



The pigmented patches on the gut of the Sudidae and Syuodonti<hu' (I'l. \ II. 

 figs. 1, 2, 4). the armature oi' the head in the Platycephalidae (PI. X. fig. 4) and 

 Trio'lidae, are examjiles of .similar larval characters in relateil familie.s. The 

 development of the anal fin before the dor.sal in the Iniomi. the migraticm of the dor.sal 

 in the Clupeidae, Albulidae, etc., may be citeil as exam])les of ilevelo]imental features 

 comnujn to a series of related families. 



