WHEEL-BEARERS 369 



rily, to a greater or less degree, retracted within the body, 

 by the inversion of the surrounding parts of the exterior, 

 while, in those genera in which it is permanently enclosed, 

 analogy requires us to consider the condition as induced 

 by a similar inversion, but of permanent duration. If 

 we imagine the head of a soft- bodied Insect-larva retracted 

 to a great degree (as is done partially by many Dipterous 

 larvae), the skin of the thoracic segments would meet to- 

 gether in front, around a purse-like opening, which would 

 be the orifice of such a buccal funnel as exists in most 

 Rotif&ra. In the latter, it is the normal condition; in the 

 former, it is merely accidental and temporary. 



We need not devote any more minute consideration to 

 the digestive apparatus in our little Brachion, but there 

 are some other points in its structure which are worth 

 noticing. In the central line of the body, just above the 

 mouth, as you see the animal in a dorsal view, there is a 

 square speck of a rich crimson hue, the edges of which, 

 when we view it under reflected light, glitter and sparkle 

 like a precious stone. But when we obtain a perfectly 

 lateral view, we perceive that the situation of this gem- 

 like speck is considerably nearer the dorsal side of the 

 shell than the mouth, and that it forms a wart-shaped 

 prominence on a large turbid mass which occupies the 

 whole front portion of the animal. By comparison of this 

 organ with the corresponding parts in other genera, there 

 is every reason to infer that this turbid mass is an enor- 

 mous brain, the nervous matter being in a very diffuse 

 condition; and that the ruby seated on it is an eye, con- 

 sisting of a crystalline lens, and a layer of crimson pig- 

 ment beneath it. 



The oval bodies that you see attached to the hinder 



