POLYGASTRIA. 



15 



with them the materials for nourishment (fig. 

 14). In the interior of the body the nutri- 

 tive sacculi appear like so many little empty 

 bags hanging from the mouth. The food of 

 the Monads seems to consist entirely of par- 

 tictes of decaying matter. 



Fig. 14. 



ft 



W' 



' 



Monas quttula, highly magnified, showing the direction 

 of the nutritive currents. 



Dental system. A very remarkable dental 

 apparatus was discovered by Ehrenberg to 

 exist in some of these diminutive beings, their 

 presence being recognised in several different 

 species, viz. Euodon cucuUus (Synonyme, Kol- 

 poda, Loxodes cuctillus), Nassula ornata, Nas- 

 sida elegans, Nassula aurea, Prorodon niveus, 

 Prorodon compressus, and others. Both in their 

 form and connexions these teeth are very remark- 

 able, presenting the appearance of a long slender 

 cylinder or hollow cone, situated at the entrance 

 of the mouth, around which they form a closely 

 approximated series (jig. 15). These teeth 



Fig. 15. 



Dental apparatus of Chilodon ornatus. 

 Ehrenberg.) 



(After 



first seized and bruised by the dental apparatus. 

 In this case the buccal cylinder first of all 

 expands in front to receive the morsel; it is 

 then narrow posteriorly : but as the aliment 

 passes onward it becomes contracted in front 

 and dilates behind, so as to push the food 

 towards the mouth. Sometimes, however, these 

 movements can be witnessed without any large 

 morsels of food being present in the dental 

 cylinder. While the mouth is kept open, 

 Monads and other animalcules may frequently 

 be seen to enter it with facility as far as the 

 intestine ; in which case the contraction of the 

 dental circlet seems to serve to prevent its re- 

 turn back again, should it try to escape in this 

 direction. 



A very remarkable circumstance observable 

 in these teeth is the rapid manner in which 

 new sets are formed as often as the fissiparous 

 habits of the animalcules render their repro- 

 duction necessary. This regeneration of whole 

 sets of teeth, a phenomenon so unusual among 

 other races of animals, is among these Infu- 

 soria a matter of every day occurrence, a new 

 set being produced whenever spontaneous di- 

 vision occurs : nay, should the animalcule be 

 mutilated so that only the hinder half of its 

 body remains, we are assured by Ehrenberg 

 that the missing portions will soon be repro- 

 duced, provided with a new mouth and circle 

 of teeth exactly similar to their predecessors ; 

 and when they spontaneously divide by trans- 

 verse fissure, a process which occupies but a 

 short space of time, the hinder portion, when 

 separated, is found to be provided with a 

 mouth and set of teeth completely organised 

 in every respect (l,fig> 16). Sometimes, in- 

 deed, they may be observed during this sepa- 

 ration of the adult animal into two young ones, 

 and the progress of the developement of the 

 wanting parts absolutely witnessed. Under 

 such circumstances Ehrenberg states, that such 

 is the rapidity of the process that the division 

 of the body, and the formation of a set of twenty 

 new teeth, may easily be accomplished in the 

 space of a couple of hours. 



are composed of a hard substance ; for when 

 the soft parts of the animalcule are crushed 

 between two plates of glass, they still remain 

 distinctly visible, proving that they are of a 

 denser texture than the rest of the body. Their 

 number varies in different genera from sixteen 

 to thirty, the former being the minimum and 

 the latter the maximum yet observed. In 

 animalcules thus provided with a dental appa- 

 ratus the pharynx seems to have little to do 

 with the act of nutrition ; indeed it frequently 

 happens that while the little creature vibrates 

 its cilia to produce the currents that bring it 

 food, its mouth is kept open and motionless, 

 so that the materials that serve for its nourish- 

 ment pass through it unobstructed : but when 

 larger morsels are to be swallowed, they are 



1. Nassula ornata, in progress of fissure. 2. Amphi- 

 leptus fasciola. 3. Trachelocerca viridis. 4. Tra- 

 chelocerca biceps. (After Ehrenberg.) 



Muscular system. In the generality of those 



