THE WHEEL ANIMALCULES 



3417 



above the alimentary canal. This class contains two orders, named the Achseta 

 and Chsetifera. In the former the mouth is placed at the apex of the proboscis, 

 which is retracted by a special muscle as in the Nemertine worms, and the ali- 

 mentary canal opens posteriorly in the front half of the body. Moreover, as the 

 name of the order indicates, the integument is without bristles. In the annexed 

 illustration,^ represents Pha- 

 scolosoma, one of the genera 

 of the order. Here the nar- 

 rowed part of the body is 

 the extended proboscis, which 

 is furnished at the tip with a 

 cluster of tentacles. A sec- 

 ond family of this order is the 

 Priapulidce, containing the 

 genus Priapulus, of which a 

 representation is given in C 

 of the figure. In this form 

 the body is short, stout, cylin- 

 drical, and furnished at the 

 tail end with a tuft of oval 

 papillae. The proboscis, 

 which in the figure is repre- 

 sented as protruded, is short, 

 stumpy, and covered ' with 

 toothed ridges. The animal 

 is found in deep water in the 

 seas of Northern Burope, 

 living in burrows on the 

 sandy bottom. 



The Chaetifera, which in 

 some respects approach the 

 Annelids, differ from the 

 Achasta in having the mouth 

 situated at the base of the 



proboscis, and the vent at the hinder end of the body, as also possessing a pair of 

 large hooks upon the front half of the lower surface. The best known-is the genus 

 Bonellia, represented at A in the above illustration. The proboscis is of great 

 size, being often many times the length of the body, and is forked at the end. The 

 males differ from the females, being minute, not more than about one-sixth of an 

 inch long, covered with cilia, and living within the kidneys of the females. 



THE WHEEL ANIMALCULES Class Rotifera 



The Rotifera or wheel animalcules are small aquatic animals, varying from 

 an eighth to the five-hundredth part of an inch in length, and derive their name 



GEPHYREAN WORMS. 



A. Bonellia; B. Phascolosoma ; C. Prtapulus. 

 (All natural size.) 



