MACRUROIDS. 193 



the fact of remaining on or near the bottem, sufficiently account for fre- 

 quency of capture. The species themselves are mostly of local distribution, 

 and it is altogether probable that most if not all of those to which wide 

 distributions have been assigned will yet have to be subdivided. 



The greatest depths from which up to this date Macruridas have been 

 obtained are the following: 1823 in the northeastern, 1875 in the north- 

 •western, 2160 in the southeastern, and 2425 fathoms in the southwestern 

 parts of the Pacific ; 2327 in the northeastern, 1870 iu the northwestern, 

 and 2650 in the southwestern portions of the Atlantic ; 1375 to 1950 in the 

 Antarctic, and 1310 fathoms in the northern sections of the Indian Ocean, 



As may be seen in various cases in the subjoined list, the vertical range 

 of a single species is sometimes more than one thousand fathoms, in one 

 instance, that o? Nematonurus annatus Giint., more than two thousand, which 

 indicates conclusively enough the ineffectual nature of pressure as a barrier 

 in the vertical distribution of species. If the general adaptability of tissues 

 and structure to changes of conditions is considered, there is no evident 

 reason for surprise in the fixct that individuals of a species are comparatively 

 indifferent to variations in pressure corresponding to hundreds or thousands 

 of fathoms of depth. Similar adaptiveness to variations in temperature is 

 no doubt possessed by most forms. 



So far as known modification by life at great depths includes the 

 acquisition of no special organs among the Macrurida3. The eyes of some 

 are enlarged, none of the known species are blind, but no special luminous 

 organs appear. The canals and glands of the lateral system have become 

 much enlarged and h'ave assumed much greater functional proniinence, appar- 

 ently without much change in structure, yet it is probable that the mucous 

 is more phosphorescent and that the glands have become flash organs in 

 various species. Some of the species have filamentary growths on the fins, 

 and in those from the greater depths the armature and the tissues are less 

 firm. The changes in the skull on account of enhanced function of the 

 lateral system are amply set forth on Plates L. and LI., the greater amount 

 of modification existing in the ridges inclosing and protecting the organs 

 of that system. 



Among the species described below there are close allies of Coryphoinoides 

 Bairdii and C. carajnmis, but all told the affinities are little closer across the 

 Caribbean with species of the Atlantic than across the Pacific with others 

 described by Alcock from the northern parts of the Indian Ocean. 



