The Unity of the Organism 



tive in nature, and among animals with rather highly de- 

 veloped nervous systems I shall illustrate by describing 

 briefly a performance witnessed by me some years ago. 

 This was the capture and engulfment of food by a nemertean 

 worm.* 



These marine worms are of considerable size, some reach- 

 ing a length of many inches, even a few feet, and ranging 

 in thickness from less than an eighth of an inch to nearly an 

 inch. Externally they give the impression of being very 

 lowly in organization, the body being devoid of limbs or 

 other appendages, and without segmentation. However, 

 when they are examined internally a surprisingly high grade 

 of organization is found, the muscular, digestive, blood and 

 nervous systems being on a par, probably, with those of 

 any invertebrates below the crustaceans and insects. The 

 nervous system, particularly the brain, is relatively large, 

 though not differentiated into diverse ganglionic masses and 

 connecting strands to the extent found in jointed worms. 

 The creatures are poorly equipped with external sense or- 

 gans, there being no tentacles nor any certain olfactory or 

 auditory organs. And eyes, when present, are so minute 

 and simple as to be without power of sight in the ordinary 

 sense; almost certainly they are mere light-perceiving or- 

 gans. 



The most distinctive anatomical feature of the nemerte- 

 ans is a very long and thin though muscular and flexible hol- 

 low tube situated at the anterior end of the animal, which 

 is usually carried stowed away in a pouch within the body. 

 While thus retracted the tube has some such relation to 

 the rest of the animal that a glove-finger would have to the 



* Greatly to my regret I am unable to say what the species or even the 

 genus was of either the nemertean or the annelid here referred to. The 

 observation was made at the Shumagin Islands, Alaska, and under cir- 

 cumstances that rendered it quite impossible to "look up" the species. 

 And my knowledge of the taxonomy of these groups of worms is alto- 

 gether too meager to enable me to identify genera even, offhand. 



