INTEODUCTION. 7 



the mastax ; and there is a posterior opening towards the dorsal surface, just above the 

 oesopliagus. 



The contained hard parts, or troiM, consist of two hammer-hke bodies, tlio mallei 

 (fig. 6, ms ; fig. 9), and of a third anvil-piece called the incus (fig. 6, is). Each malleus 

 has for its head or uncus (figs. 6, 7, 9, us) a piece which, when spread out by pressure, 

 is like a comb with five unequal teeth (fig. 8, ms), but which, under ordinary circumstances, 

 is much curved, so as to bring the teeth close together. 



The handle of each of these hammers is a single stout piece called the manuhrium 

 (figs. 6, 7, 8, 9, vim). The anvil or incus roughly resembles a triangular prism, of which 

 one end (the dorsal one) has been tapered to a point (fig. 10). It is divided into two equal 

 pieces, the rami (figs. 6, 7, rs), by a cut from the dorsal to the ventral surface, so as to leave 

 them just attached to each other at the bottom of the broader end. The two rami rest 

 there on what looks like a stem, the fulcrum, (figs. C, 7, fm), but which viewed laterally is 

 seen to be a slender plate (fig. 10, fm). 



Muscles, springing from the walls of the mastax, are attached to various parts of the 

 mallei and rami, and act so as to cause the unci to approach and recede from each other. 

 But each uncus is fastened to the corresponding ramus ; and, in consequence, as the mallei 

 recede the rami are opened, and when the mallei approach each other the rami are closed. ' 



From these arrangements it results that all the food which falls from the buccal 

 funnel into the mastax, is first torn by the sharp points of the mici and then crushed 

 between the opposing surfaces of the rami. On passing the rami, the food enters at once 



into the oesophagus. 



The CEsophagtis. 



The (XsopJiagus (fig. 2, ce) is a short tiibe, with thick walls, connecting the mastax 

 with the stomach. The thiclmess of the walls may be readily seen by feeding BracJiionus 

 with carmine, and watchmg the stream of coloured particles trickle through the ffiso- 

 phagus into the stomach. Their course, in a narrow central line, shows clearly the small 

 dimensions of the passage. 



There is always an appearance of water flowing through the cesophagus, even when, 

 the animal has withdrawn its head into the lorica, and when of course the action of the 

 ciliary wreath has ceased. This appearance seems to be due to minute cilia lining 

 the ojsophagus, which by their joint rhythmical action give rise to illusory waves much 

 larger than any real waves could be. That this explanation is not a mere guess will be 

 shown farther on in the case of the Floscules. 



The Glands. 



Seated near the top of the mastax, and on either side of the buccal funnel, are two 

 clear vesicular organs ; which are possibly salivary glands (fig. 2, sg), and are unusually 

 large in Brachionus. They consist of two or three lobes on either side, and are best 

 seen from the ventral side, as the buccal funnel enters the mastax, a httle below the 

 summit, on that side. 



There is a pair of glands called the gastric glands (figs. 1, 2, gg) placed at the 

 anterior end of the stomach, and on either side of it. They exhibit cells with central 

 nuclei imbedded in a granular substance. Each has a long, wide, nucleated duct 

 comiecting it with the upper end of the stomach. They probably perform the func- 

 tion of a rudimentary liver, and possibly cause, by their secretion, the peculiar yellow- 

 brown colour which is so frequently met with in the stomach. The foot-glands have 

 already been described in p. G. 



The StoJiiach and Intestine. 

 The stomach (figs. 1 , 2, s) is a simple sack, with thick cellular walls, which arc frequently 



" For a full description of the complex action of the trophi see Mr. Gosse's paper " On the Struc- 

 ture, Functions, and Homologies of the Manducatory Organs in the class Rotifcra," Vhil. Trans. 185G, 

 p. 410. 



