Flatworms and Threadworms 307 



the posterior end is 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 person. The parasite produces no known symptoms in 

 the patient, although patients who have been infected have become 

 anaemic and suffered with diarrhoea. 



Dicotophyme renale is a worm, 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) is also called Gigantorhynchus or 

 Echinorhynchus. These are quite common in the intestine of the hog, 

 where they attach themselves by means of a protrusible proboscis 

 covered with hooks. In the old world the larva develops in cockroach 

 grubs, while in America the larva develops 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. 



Cerebratulus ( ), and Micrura ( ), 



(Fig. 195), are the usual examples of marine Nemertinae. Other forms 

 are not common. Malacobdella ( ) is parasitic in 



some mollusks. 



The Nemertinae are considered the lowest form of animal life in 

 which the blood-vascular system appears. There is a definite mesoderm 

 and a nervous and an excretory system quite like those in flatworms, 

 but they all have a long proboscis just above the digestive tract which 

 lies within a sheath. This can be everted. The body is covered with 



