LUCERMARIJi AND TUEIR ALLIES. 105 



umbella. By fits and starts these were very active, moving rapidly by means of 

 the cilium. 



201 (B). We do not believe that it has been observed to what extent vibratile 

 cilia are individualistic in their movements, at times, just as an arm or a leg is 

 individualized. Cilia are commonly treated of like masses of men in an army, all 

 moving to one determined end ; as if the recorder of their movements did not 

 think that the animal possessing them had the discriminating power of controlling 

 the actions of any one separately. As well might one claim that the numerous 

 legs of a Centipede are not capable of individual control. In contravention of 

 such a mistaken assumption, we have been at some pains to illustrate the varying 

 attitudes of the cilia [Ji(j. 109, iv) of the generative organ at a time when they 

 were in a less active state than usual. Some of them project in rigid, straight 

 lines from their bases ; some again are straight at the base and undulating rapidly 

 near the tip ; others are in long curves from end to end, while here and there 

 one vibrates in short, sharp curves throughout its length. These motions may be, 

 by some persons, attributed to irritability, such as is often observed in recently 

 killed animals ; but the animal is fully alive in this case. We are well aware of 

 the fact that we, ourselves, are unconscious of the movements of the vibratile cilia 

 in our own body, but, on the other hand, no one, who is well versed in the habits 

 of the Protozoa, will deny that the cilia and flagella of those creatures are to them 

 what the arms and legs are to man. We claim, therefore, here, that the pheno- 

 mena observed in Lucernarise furnish just reason for assuming that the vibratile 

 cilia are, at least in a measure, individually controllable. 



It will be observed that our figures represent the cilia as having an equal thick- 

 ness from base to tip. This we believe to be the fact in many other animals, but 

 it is not generally so represented, because the tips of the cilia are usually so much 

 more active than toward the base as. to mislead one into inferring that they are 

 thinnest there, since that part is not so easily detected. 



201 (C). The genital saccule-t differ so little from the circumoral parietes in the 

 histological elements of the walls, that all that is necessary to characterize them 

 has been incorporated in the section (§ 18) where their general structure is 

 described. 



§ 26. Histologi/ of the Tenfxides {figs. 88, 89, 90, 91, 92, 93). 



202. The Ect02)Jtragma of (he Tentacles (5[ 96). — Notwithstanding the very 

 extensive modifications to which this layer is subjected, in the different regions 

 of the body, whether as the ectophragma proper on the posterior face of the 

 umbella, or in the thickened peduncular disk, or as the thin opsopliragma in 

 front, or its prolongation on the shafts of the tentacles, or its great thickening 

 mass on the globose tips of the tentacles, everywhere it retains its simple character 

 as a single stratum of cells. No amount of differentiation, whether in reference 

 to form or function, obliterates, or even disguises, that one unvarying, dominant 

 character. These diversities are brought about by the least possible means; no 

 repetitions, no circumambient or collateral api)liauces are connected witli the pro- 



14 AprO, 1878. 



