72 POND LIFE 



case the creature divides into more than one part, each of which 

 ultimately becomes a fresh individual. Planarians seem to be 

 highly intelligent, but many more experiments must be carried 

 out before this can be definitely stated. Comparatively little 

 is known as to their habits and life histories, and so a large 

 field of research is open to the ardent pond-hunter. 



Wishing the Planarians the best of luck, we must unwillingly 

 turn to the Nematode worms, which are the cause of very many 

 serious illnesses to higher animals, man included. 



Thread-worms, as they are popularly known, frequent ponds 

 and ditches. Some are minute, others large. 



In Ascaris lumbricoides the male is 4" to 6" long, whilst the 

 female is 10" to 14". It is said that in Finland very few people 

 are free from the companionship of this unwelcome stranger. As 

 if to add insult to injury, even the examination of Ascaris lum- 

 bricoides is not unf raught with danger, for it is able to give off 

 an odour of surprising power, so irritating, indeed, that it 

 produces catarrhal symptoms. 



Rhabdonema nigrovenosum, another thread-worm, inhabits 

 the excreta of frogs. After a very short time the male and 

 female worms meet and pair. The fertilised eggs eventually 

 hatch and the youngsters with practical filial devotion devour 

 the internal organs of the mother, thereby causing her death. 

 The offspring then hurriedly decamp, and wait patiently until 

 some frog appears and foolishly swallows them. Thus having 

 made an entry into their host, they waste little time in making 

 their way to the lungs : here they live happily and comfortably, 

 mature and fertilise each other, resulting in a fresh generation 

 of embryos. These eventually escape into the water and find 

 their way to frogs' excrements. Male and female worms again 

 meet, and the story is repeated. 



Nematomorpha are very similar in appearance to the nema- 

 tode worms, in fact up to quite recently they were classified as 

 members of this family. We need not waste much time in 

 describing the creature, for we are all familiar with the thread- 

 like little worms seen in every pond. 



The life history of one member of the Gordius is so unique 

 that it deserves some notice. The Gordius is the only fresh- 

 water family of the Nematomorpha. The male is distinguished 

 from the female by its forked tail, and by its colour. In April 

 the males and females meet and fertilisation takes place. 

 Subsequently the eggs are laid in long threads, and after some 

 weeks the larvae appear. These little creatures are furnished 

 with boring appliances, which they deftly use in order to 

 obtain an entry into the body of a young (larva) of an alderfly. 



