HYDATINA. 



151 



III.— HYDATINA. 



Phylum 



ROTIFERA. 



Hydatina senta is a small microscopic animal very commonly 

 found in freshwater ponds and streams. Its body is transparent and 

 elongated. At the blunt or oral end is a ciliated funnel-like depression, 

 the vestibule^ at the bottom of which is the inouth. The edge of the 

 vestibule is fringed with a band consisting of specially long cilia, which 

 is known as the cingulum. Further towards the centre of the vestibule 

 broken row of 



Fig. 85.— Ventral View of Hydatina 

 Senta x 40. 



(After Pt atf). 



Trochus.__ 



CEsophagus. 



Right 



Hepatic Gland.. 



Excretory. 



Tubule. 



Cingulum. 



IS a 



longer cilia, called the 

 trochtis, whilst the 

 groove between trochus 

 and cingulum is raised 

 into several lobes bear- 

 ing styles. This Com- 

 plex apparatus is often 

 called the wreath and 

 serves for locomotion 

 and for ingestion of 

 food. The aboral end 

 is tapering and termin- 

 ates in a bilobed foot 

 endowed with a pair of 

 adhesive glands. The 

 body is enveloped in 

 a thin delicate cuticle 

 covering a simple ecto- 

 derm. The mouth leads 

 into a maslax which 

 is a complex grinding 

 apparatus containing 

 chitinous teeth. From 

 this an cesophagtis is 

 continued into a large 

 digestive stomach fol- 

 lowed by an hitestine. 

 The intestine terminates 

 in an anus^ situated 



not at the aboral end but on one surface, usually termed dorsal. Two 

 salivary glatids open into the mastax, and two hepatic ox , digestive 

 glands discharge their fluid into the stomach. 



The alimentary canal hangs freely in the cavity of the body, which 

 is filled with colourless fluid. This body-cavity is traversed by connec- 

 tive tissue and muscle fibres, but has no coelomic lining. Throughout 

 its course, laterally to the alimentary canal, is a pair of excretory 

 tubules which bear branches terminating in closed flame-cell sacs. Each 

 tubule opens behind into the urinary bladder with a single aperture to 

 the exterior near the anus, forming a cloaca. Anteriorly the two tubules 



Ovary, 



Yolk Gland. 



Adhesive Gland. 



Cloaca. 



