824 PROFESSOR J. STEPHENSON ON 



With regard to the sedentary habit itself, it is possible to hold that this, rather than 

 the active free-living condition, is primitive ; and consequently that the absence of 

 certain features, which when present are correlated with an active habit, may, in 

 sedentary forms, be due not to degeneration, but to the persistence of an original 

 state. The argument for the primitiveness of a sedentary habit has recently been 

 presented by Willey (57) ; it would be superfluous, therefore, on my part to discuss the 

 point, or even to repeat at length his presentation of the subject ; all that can be done 

 is to transcribe a few passages to indicate the character of his argument, and for the 

 rest to refer the reader to his book. 



Willey, writing from a physiological point of view, divides animals into phanerozoic 

 (diurnal, positively heliotropic) and cryptozoic (crepuscular, nocturnal, and subterranean 

 — in general terms, negatively heliotropic) forms, and states that the animal kingdom 

 as a whole seems to show negative phototaxis. " A journey through any tropical 

 forest or jungle, or even a little retlectiou, will, I think, suffice to convince one that 

 while the vegetation is luxuriantly phanerotactic, animal life is predominantly crypto- 

 tactic. The jungle is like the desert and the ocean, to all superficial appearances 

 frequently devoid of animal life. This is possibly not the impression which one would 

 receive from the perusal of faunistic works ; but it is certainly that which is produced 

 by observations in the open, and I regard it as one of the radical bionomical or habitual 

 diiferences between animals and plants." 



And later, "it is doubtless in virtue of this singular property of concealment that 

 so many of the primitive forms (he is speaking of the Arthropoda) have survived at the 

 present day to be at once the delight and bewilderment of the systematist." " Predatory 

 aquatic animals . . . may be described as phanerozoic ; but we may confidently assert 

 that in all cases a definite cryptotactic bias of varying intensity could be demonstrated." 

 Finally, " the basic quality underlying all animal life is the cryptic, the fear of the sun." 



This tendency to concealment is, of course, related to the sedentary habit ; but about 

 the latter there is more to be said. " The remarkable prevalence of the sedentary habit 

 amongst the lower {i.e. invertebrate) animals seems to indicate that something 

 peculiarly primordial lies at the back of the phenomenon." Fixation is an extreme 

 form of the sedentary habit ; the principle which lies at the back of both is expressed 

 in the term " stereotropism " {i.e. the tendency to cling to a surface), invented by J. Loeb. 



" Many cases amongst the Annelid worms could be instanced where stereotropism 

 and pleotropism (the free-swimming habit) exist side by side, the latter frequently only 

 manifesting itself at the breeding or swarming season, as with epigamous Nereids." 

 Eisig's observations have shown that free swimming results from a greater violence 

 of the same movements that are used in crawling; "when the amplitude of these 

 undulations surpasses a certain magnitude, the rapidity of movement is thereby increased 

 to such an extent that the animal rises from the bottom and swims through the water." 

 EisiG concludes that the stereotropic movement (on the bottom) is secondary as 

 compared with the pleotropic movement (through the water), and is derived by 



