146 Comparative Animal Physiology 



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estimated the pores of the sacs of Chaetopterus to be about 40A in diameter. 

 Certain vertebrates, such as the baleen whale, many fishes, and even a few 

 birds which capture insects on the wing, may be considered filter feeders, in 

 which locomotor and sometimes pharyngeal muscular activity serves as the 

 force involved in filtration. 



SETOSE. This type of mechanism is characteristic of numerous aquatic 

 crustaceans such as Daphnia, copepods, cirripedes, ostracods, and larvae of 

 certain insects such as mosquitoes and mayflies. Movements of certain ap- 

 pendages with their fringes of setae sweep particle-laden water into certain 

 areas among the appendages where setae strain out the particulate matter. 

 The particles are then bound into larger masses by a viscid secretion and 

 carried to the mouth. 



Mechanisms for Dealing with Large Particles or Masses. Mechanisms of 

 this type are subdivided by Yonge into three groups: 



FOR SWALLOWING INACTIVE FOOD. Organisms possessing mechanisms for 

 swallowing inactive food, such as mud, are typically burrowing forms, rather 

 sluggish in habit. Included in this category are certain holothuroids which use 

 their tentacles to force mud into their digestive tracts. Annehds such as 

 Lwnbricus and Arenicola possess eversible pharynges for this purpose; echino- 

 derms such as spatangids use their tube feet; and burrowing crustaceans such 

 as Upogehia and Callianassa use their mouthparts. The organic content of the 

 mud is utilized, and the residue is ejected in the feces. 



FOR SCRAPING AND BORING. Thcsc mcchanisms are found in animals char- 

 acterized by more or less continuous feeding. They usually have organs for 

 attachment to permit the special apparatus for scraping or boring to be used 

 effectively. Examples of this type of mechanism are the Aristotle's lanterns of 

 echinoids, the radular apparatus of many molluscs, the special boring valves of 

 Teredo, and the heavy mouthparts of termites. 



FOR SEIZING PREY. Mcchanisms for seizing prey are further subdivided by 

 Yonge into three groups: (1) For seizing only. These would include the 

 pseudopodia of amoebae, the impaling proboscis of Didinium, nematocysts of 

 coelenterate tentacles, lasso-cells of ctenophore tentacles, the turbellarian 

 pharynx, the jawed pharynges of many polychaetes, the chitinous hooks of 

 chaetognaths, the teeth and radula of some gastropods, and the suction mech- 

 anism of feeding of septibranchs. (2) For seizing and masticating. Examples 

 of these are the jaws and radulae of many molluscs; the jaws and other mouth- 

 parts of crustaceans, insects, arachnids, and myriapods; and the toothed jaws of 

 vertebrates. 



In the jawed vertebrates or gnathostomes the anterior teeth often bite or 

 gnaw, and posterior teeth masticate; however, there is much variety, ranging 

 from amphibians and billed birds which chew very little, to the ungulates 

 with heavy chewing molars. 



(3) For seizing followed by external digestion. This type is illustrated by 

 the sarcodinian, Vampyrella, which digests a hole through the walls of the 

 algae on which it feeds; by Asterias, whose everted stomach kills and digests 

 its prey; by many carnivorous gastropods; by Sepia; and by many insects such 

 as Dytiscus larvae. 



Mechanisms for Taking in Fluids and Soft Tissues. Such mechanisms 

 usually include a pumping muscular pharynx. There may be chitinous jaws or 



