PHYLA NEMATHELMINTHES, NEMATOMORPHA, AND ACANTHOCEPHALA 



153 



structurally indistinguishable, but they dif- 

 fer physiologically in that the human ascaris 

 eggs do not usually produce mature worms 

 in pigs and vice versa. 



How does the intestinal 

 parasite resist digestion? 



This is a very interesting and perplexing 

 question. That they resist digestion when 

 alive is common knowledge. However the 

 mechanism is by no means clear although 

 much research has been done on it. There 

 are two schools of thought: (1) that there 

 is a passive anti-enzyme action, due to the 

 chemical constitution of the parasite, which 

 makes it resistant to enzyme action, and (2) 

 that the parasite secretes chemical sub- 

 stances by means of which the host's diges- 

 tive enzymes are neutralized or in- 

 hibited. 



In the case of nematodes there is some 

 experimental evidence for the production of 

 enzyme-inhibiting substances. More specifi- 

 cally, there is recent proof of an interfer- 

 ence with the digestion of dietary protein 

 by intestinal juices because of the anti- 

 enzymatic action of the ascaris. This strongly 

 suggests that there is an anti-enzyme se- 

 creted by the ascaris, which counteracts the 

 effect of the host's digestive enzymes. Of 

 course, the thick cuticle covering this worm 

 provides some protection from the host's 

 digestive juices. 



The results of investigations on the resist- 

 ance of tapeworms to digestion have been 

 inconclusive. 



Free-living roundworms 



The vinegar eel 



The vinegar eel Turbatrix (Anguillula) 

 aceti is a free-living nematode, easily ob- 

 tained at any time of the year from the bot- 

 tom of a cider vinegar barrel. It is visible to 

 the naked eye when held before a bright 

 light and exhibits characteristic nematode 



movements. Heating the vinegar for a min- 

 ute kills and straightens vinegar eels, and 

 clearing them in phenol, after fixing, reveals 

 the internal organs. 



The female worm is about 2 mm. and 

 the male about 1.4 mm. in length. Most of 

 the anatomical features of a female are 

 shown in Fig. 80. The eggs are not only 

 fertilized within the body of the female but 

 also develop there. The thin egg membrane 

 ruptures in the uterus and the young are 

 born in an active condition, that is, the 

 vinegar eel is ovoviviparous. One female 

 may produce as many as 45 larvae. Males 

 and females are equal in number; they may 

 live for 10 months or more. 



Other free-living roiindworins 



Free-living nematodes are mostly small, 

 a large specimen being only one cm. in 

 length. Many of them possess an oral spear 

 with which they puncture the roots of 

 plants, badly injuring economically valu- 

 able species, as well as others. Several hun- 

 dred millions of dollars of damage result 

 every year from these attacks. They live in 

 almost every conceivable type of environ- 

 ment, such as wet sand or mud, aquatic 

 vegetation, standing or running water, the 

 soil, the sea, tap water, fruit juices, and 

 moist places almost everywhere. They have 

 been found in such varied habitats as Pike's 

 Peak, Alpine snows, the Antarctic Ocean, 

 and in hot springs. "If all the matter in the 

 universe, except the nematodes, were swept 

 away, our world would still be dimly recog- 

 nizable, and if, as disembodied spirits, we 

 could then investigate it, we should find its 

 mountains, hills, vales, rivers, lakes, and 

 oceans represented by a film of nematodes. 

 The location of towns would be decipher- 

 able, since for every massing of human be- 

 ings there would be a corresponding massing 

 of certain nematodes. Trees would still stand 

 in ghostly rows representing our streets and 

 highways. The location of the various plants 

 and animals would still be decipherable, 

 and, had we sufficient knowledge, in many 



