306 GENERAL BIOLOGY 



the infected person of its own accord. Few of these have been found 

 in America. 



Trichocephalus dispar (Fig. 193), or whip-worm, is found in the 

 caecum and large intestine of man. It is 4 to 5 cm. in length, the male 

 being a trifle shorter than the female. The parasite is remarkable in 

 that there is a great differentiation between the two ends of the body. 

 The anterior end, which forms about three-fifths of the body, is very 

 thin and hair-like, while the posterior portion is thick, and, in the female, 

 conical and pointed. In the male it is blunter and rolled like a spring. 

 The eggs are lemon-shaped, 0.05 mm. in length. Each has a button-like 

 projection. There may be as many as a thousand parasites in one per- 

 son. The parasite produces no known symptoms in the patient, although, 

 patients who have been infected have become anaemic and suffered with 

 diarrhoea. 



Dicotophyme renale, the male of which is over a foot long and the 

 female over three feet. These are seldom met with, but when present 

 may destroy the entire kidney. 



Anguillula aceti'or (vinegar eel) has been found in the urine of man, 

 although it is supposed to have been in the bottle in which the urine was 

 collected. 



Strongyloides intestinalis is found in the small intestines of man in 

 the tropics. Three per cent of the medical patients of the Isthmus of 

 Panama were found to be infected, and 20 to 30 per cent of the insane 

 division. 



Acanthocephalus (thorn-headed worms) are also called Giganto- 

 rhynchus or Echinorhynchus. These are quite common in the intestine 

 of the hog, where they attach themselves by means of a protrusible pro- 

 boscis covered with hooks. In the old world the larva develops in cock- 

 roach grubs, while in America the larva devlops in the June bug. 



The Acanthocephalia are distinguished from the Nematodes and 

 the Nematomorpha by the presence of a proboscis and the absence, of an 

 alimentary canal. 



! ; INTERMEDIATE AND UNCERTAIN FORMS 



In addition to the rather definite groups of worms mentioned in this 

 book, there are also various forms of uncertain position. 



The term Mesozoa (Fig. 194) (Gr. mesos, middle zoon, animal) 

 is often used as a general grouping for the three following families of 

 parasites: (1) Dicyemidae, (2) Orthonectidae, (3) Heterocyemidae. 



They are called Mesozoa because they are regarded as intermediate 

 forms between the protozoa and the metazoa. They are closely allied 

 to the flat worms. 



The Nemertinae (Gr. nemertes, true), are usually placed with the 

 flat worms. They may reach a length of ninety feet and are mostly 

 marine, though a few live in fresh water and in moist earth. 



