45 s 



WORMS. 



g 



from 3 to over 6 inches. It is a long, flat, whitish-coloured creature, occurring on 

 muddy ground and between the branches of coral ; and has received its name from 

 the habit of breaking up into pieces at the least touch. The 

 - vitality of the severed pieces is so great that the head end 



nas t ne power to re-form a new tail, and the tail end a new 

 head, and the intermediate pieces a new head and tail. 

 Another common kind is Polia crucigera, so-called because 

 its greenish body is marked with five longitudinal white 

 bands and transverse white stripes, forming together a 

 series of crosses. These worms are long and slender, reaching 

 a length of about 16 inchee. The proboscis, moreover, when 

 protruded, adds another 6 inches to their extent. They are 

 found most abundantly in pieces of rock riddled with holes 

 and galleries by boring sponges, and they also intertwine 

 themselves amongst the prongs of branching-corals, as shown 

 in the illustration. 



Most marine iiemertines prefer rather shallow water; 

 but some occur at considerable depths ; and a pelagic species 

 from the Indian Ocean, originally described as a mollusc, 

 under the name Pterosoma planum, is a transparent 

 creature, whose internal organs, especially the chestnut- 

 brown digestive apparatus, are visible through the colour- 

 less integument. The body diminishes from the front 

 towards the hinder end, and at the sides is marked out by 

 deep notches into a series of five lobes, of which the first 

 pair are enormously large, and have the form of two 

 semicircular wings. The use of these is doubtless to enable 

 the creature to float or swim in the water. All the fore- 

 going are free living types, but we now come to forms 

 (Malacobdella) not unfrequently found living parasitically 

 under the gills of various marine molluscs. In these, the 

 body is short and broad and capable of but little change 

 in shape at its hinder end ; it is furnished with a sucking 

 apparatus, by means of which the animal adheres to its 

 host. As stated above, almost all nemertines are of separate 

 sexes ; and in some marine species the development of the 

 young is so remarkable that it is impossible to pass it by 

 without notice. The young which issue from the egg are 

 so unlike the parent, that no one would at first sight suppose 

 them to belong to this group. The larva, as shown on 

 p. 461, bears some resemblance to a helmet, and has been 

 named Pilidium. This creature, which is covered with 

 cilia, swims near the shore for some time, while the young 

 nemertine is developed inside. As soon as this has acquired 

 A FOUR- EYED NEMERTINE, its ciu and attained a cer tain stage of maturity, it breaks 



Tetrastemma obscurum . . c TP 



(enlarged). from the pilidium and starts an independent lire. 





