156 



Platyhelminihs. 



Tlie Nemertines are for the most part marine, living usually at 

 tlie bottom of the sea. Some are fresh-water or terrestrial. They 

 feed upon other animals. 



One form living in European seas, Linens longissimus, sometimes attains 

 a length of 13 m., -with a breadth of 8 m/m. Most species are a few centi- 

 metres, some only a few millimetres long. 



Appendix to the Platyhelminths. 



Botifera {TFheel Animalcules). 



The Rotifers are usually microscopic creatures, which in size, 

 habitat, and mode of life resemble the Infusoria. The posterior part 

 of the body, the foot, is narrowed, separated from the trunk, 

 and provided with a pair of short appendages or with an adhesive 

 disc at the tip. At the anterior end, there is a more or less 

 well-developed (sometimes scalloped) trochus, the rotatory organ, 

 whose edge is beset with strong cilia. It serves two purposes ; in the 

 first place it is of use in swimming, and secondly, by means of the 



Fig. 118. A Diagram of the anatomy of a female Rotifer, lateral view. B the 

 male, a anus, c ganglion, rh contractile bladder, d yolk sae, ex excretory organ, h ovary, 

 m stomach, o mouth, oc eye, r wheel organ, « pharynx, t testis, 3 male aperture. — Orig. 

 (with assistance from Plate's figures). 



currents set up by it, small particles are driven into the under- 

 lying mouth. The trunk, in some forms, is covered by a hard 

 chitinous shield, the lorica (a specialised thickening of the 

 cuticle covering the whole body), which maybe armed with spines. 

 In other cases both trunk and foot exhibit delicate constrictions 

 which simulate a segmentation, but there is never a corre- 

 sponding arrangement internally. The foot is often articulated 

 with the body, so that by its help the animal can crawl about like 



