326 



ZOOLOGY 



SECT. 



bearing long stiff cilia like the pseudopodia of the Heliozoa. The 

 single circlet may be folded upon itself, or a second type may be 

 produced by the addition of a second circlet within and parallel to 

 the first. The mouth in this case is always placed between the two 

 circlets on the ventral side (Fig. 272), so that the inner or anterior 

 circlet is pre-oral and corresponds with the chief ciliary band 

 of a trochophore larva, while the outer or posterior circlet corre- 

 sponds with the post-oral band found in many worm-larvse. In the 

 curious globular Trochosphcera (Fig. 275, 3) there is a single 

 equatorial circlet, which is pre-oral, and a few post-oral cilia : here 

 the correspondence with the typical worm-larva is singularly 

 close. Lastly, both the pre- and post-oral circlets may be pro- 

 duced into more or less complex lobes, as in Melicerta (Fig. 274, 4), 

 or may be interrupted as in Brachionus, in which the pre-oral 

 circlet is represented by three distinct lobes, or as in Pedalion, 

 in which both circlets are divided into right and left moieties. 

 In one genus the trochal disc is absent. 



m, 



Flu. 27C. Typical forms of mastax. A, forcipate type ; B, incudate type ; C, ramate type ; 

 /. fulcrum ; m. manubrium ; r. rarnus ; . uncus. (After Hudson and Gosse.) 



Digestive Organs. The typical form of mastax or pharyngeal 

 mill is that described in Brachionus (Fig. 270). There is an unpaired 

 incus consisting of a short stem or fulcrum (/.) and of two broad 

 branches or rami (r.), and a pair of mallei, each consisting of a 

 stout handle or manubrium (m.) and a broad, toothed head or 

 uncus (u.). In some forms all the parts of the apparatus become 

 very slender, the incus assuming the form of forceps (Fig. 276, A). 

 Or the mallei may be absent and the two rami movable upon 

 one another so as to convert the incus into a pair of forceps (B) 

 used to seize prey, the mastax being in this case protrusible. 

 Lastly, the fulcrum and manubrium may be absent, and the unci 

 and rami very strong and massive (C). Glands, supposed to be 

 salivary, open into the mastax or oesophagus. 



The stomach is always large, and usually has a pair of digestive 

 glands opening into it : it may pass insensibly into the intestine, 



