DISTRIBUTION OF COEALS. 241 



have been expected. In ninety-seven hauls, made in depths ranging 

 from ten to five hundred fathoms, positive results, with a capture 

 of some twenty specimens, belonging to thirteen or more species, 

 were obtained eleven times ; in one hundred and sixty-five hauls, 

 made in water of from five hundred to twenty-nine hundred fath- 

 oms, similar results, with a capture of sixty specimens, representing 

 twenty-one species, were obtained fourteen times. In the deeper 

 dredgings, however, the casting of the net was protracted over a 

 greater period of time, and, consequently, covered more space than 

 in the shallower ones, and due allowance should be made for this 

 circumstance. The relative abundance of the deep-sea Actinias is 

 shown by the fact that not infrequently two or more species, or in- 

 dividuals belonging to a single species, are found associated in the 

 same locality. The greatest depth from which any species has thus 

 far been obtained is twenty-nine hundred fathoms (Antheomorphe 

 elegans). 



Professor Hertwig, from the data collected by the " Challenger," 

 believes it may be safely assumed that, the greater the depth of 

 water the greater is the variation between the deep-sea forms and 

 those of the coast-line. Thus, it is shown that, of the thirteen spe- 

 cies and twelve genera obtained from a zone of ten to five hundred 

 fathoms, only five species and two genera were found to be new, or 

 as not essentially belonging to the coast ; on the other hand, of the 

 twenty- one species and seventeen genera obtained from a depth 

 of from five hundred to twenty-nine hundred fathoms, eleven of the 

 genera, and, with one exception, all of the species, were new. 88 The 

 same authority finds that increased depth exerts a remarkable influ- 

 ence in modifying the organisation of many of the forms. Thus, 

 the tentacles exhibit a distinct retrograde formation, or degenera- 

 tion, being first transformed into tubes, and ultimately into simple 

 openings in the oral disk. " In Paractis tubulifera (depth eighteen 

 hundred and seventy-five fathoms) the tentacles have the same con- 

 stitution as in the majority of Actinias, except in one point, that the 

 terminal opening, which is usually small or entirely wanting, gapes 

 widely. In Polysiphonia tuberosa (five hundred and sixty-five 

 fathoms) the tentacles have become short, slightly movable, wide- 

 mouthed tubes; in Sicyonis crassa (sixteen hundred fathoms) they 

 are small, wart-like rings, and in Polystomidium patens (eighteen 

 hundred and twenty-five fathoms) and Polyopis striata (twenty-one 



