CILIA. 



633 



the internal surface of the intestine and ccecal 

 appendages of the Aphrodita, within the sto- 

 mach and coeca of the Asterias, in the stomach 

 of the Actinia, in the canals of the Sponge, 

 which no doubt belong partly to the alimentary 

 system, and in the mouth, throat, stomach, and 

 intestine of several Polypi. It is not easy to 

 see the purpose of the motion in all these 

 cases. In some it may merely convey secreted 

 matters along the surface of the lining mem- 

 brane; in Polypi it agitates the food within the 

 alimentary cavity, and in several instances it 

 seems almost to serve in place of ordinary 

 deglutition, to carry food into the stomach. 



d. Reproductive organs. The phenomenon 

 occurs on the mucous membrane of the Fallo- 

 pian tubes, uterus, and vagina of Mammalia, and 

 of the oviduct in Birds and Reptiles. From 

 the direction of the impulsion being from 

 within outwards, it is difficult in the meantime 

 to assign any other office to the cilia in this 

 situation than that of conveying outwards the 

 secretion of the membrane, unless we suppose 

 that it also brings down the ovum. 



The phenomenon has been sought for in 

 other parts of the body, but hitherto without 

 success. Purkinje and Valentin state that on 

 examination they could not find it in the fol- 

 lowing parts of vertebrated animals, viz. the 

 skin, serous membrane, the alimentary canal, 

 (except the mouth and gullet of Reptiles,) the 

 gall-bladder, the biliary and pancreatic ducts, the 

 urinary organs, the seminal vesicles and ducts, 

 the conjunctiva, cornea, and iris, the internal 

 surface of the bloodvessels, the globules of 

 the blood and lymph, the chorion, amnion, 

 allantois, and yolk-sac of Birds. I have also 

 repeatedly examined the foetal membranes of 

 the common Fowl, and with the same result. 



3. Of the ciliary motion in the embryo. 

 According to Purkinje and Valentin the ciliary 

 motion of the genital mucous membrane does 

 not appeal' in the foetus, nor until the animals 

 have made some approach to the adult state; 

 that of the respiratory passages on the other 

 hand becomes apparent in the embryo long 

 before it attains maturity. The ciliary motion, 

 however, to which we would here refer is that 

 which occurs at a much earlier period on the 

 surface of the embryo of many animals, and 

 generally causes it to perform a rotatory move- 

 ment within the ovum. It has now been ob- 

 served in the ova of Batrachia, Mollusca, Ac- 

 tiniae, Polypi, Sponges, and Infusoria. \Vhile 

 the embryo is contained within the ovum, the 

 cilia produce a current in a certain direction 

 along its surface, or cause the whole embryo 

 to move in the opposite direction ; hence the 

 very remarkable rotatory motion which occurs 

 in many instances, and which is so well marked 

 in the Snail. When it has escaped from the 

 egg, the embryo moves about in the water by 

 means of the cilia, as happens also with the 

 naked gemmules of the Sponge after they are 

 discharged from the parent. The ciliary mo- 

 tion is subservient to the respiration of the 

 embryo, by renewing the contact of the water 

 or fluid contained in the egg on the respiring 

 surface, and in some instances, the Mollusca 



VOL. i. 



for example, the motion is observed to be 

 especially strong at the part where the respira- 

 tory organ is afterwards developed. When the 

 embryo quits the egg, the cilia serve also for 

 locomotion, and by this provision the gem- 

 mules of fixed zoophytes are disseminated, and 

 conveyed to situations suitable for their future 

 growth. 



4. Figure, structure, and arrangement of 

 the cilia in general. The cilia are best seen 

 when their motion slackens ; their shape, size, 

 arrangement, and manner of moving may then 

 be distinguished with tolerable accuracy, at 

 least in the larger sort. Their figure is in 

 general that of slender, conical, or sometimes 

 slightly flattened filaments, broader at the base 

 or root, and tapering gradually to the point. 

 Their size differs greatly on different parts even 

 of the same animal, but on corresponding 

 parts of different individuals of the same 

 species their size seems to be the same. The 

 largest I have measured are those on the point 

 or angle of the branchial laminae in the Buc- 

 cinum undatum ; they are at least 3 g of an inch 

 long. I have not attempted to determine the 

 exact size of the smallest, but Purkinje and 

 Valentin state it at 0.000075 of an inch, while 

 they make the largest they have met with only 

 0.000908 in., which is considerably less than I 

 have found them ; but they had no opportunity 

 of examining marine animals, in which, gene- 

 rally speaking, the largest cilia are met with. 

 In the Sea-mussel the darker-coloured cilia are 

 about ^ of an inch long, the others consider- 

 ably less. 



The cilia are very generally arranged in re- 

 gular order. In some cases they are placed in 

 straight rows, as on the gills of the Mussel; in 

 others they form circles or spiral lines, as in 

 many Infusoria; and Purkinje and Valentin 

 state that in animals of the higher orders the 

 most prevalent mode of arrangement is in spiral 

 lines or ridges. They are generally set close 

 together in the same row ; on the gills of the 

 Sea-mussel I find there are seven or eight of the 

 larger cilia in the length of -^ of an inch, or 

 about seven or eight thousand to the length of 

 an inch, but in other cases there are many 

 more. In some instances they are erect, or at 

 right angles to the surface on which they are 

 planted, in others inclined, and then it would 

 seem that the inclination is in the direction of 

 the currents which they produce. In some 

 parts they are straight, in others curved, not 

 only when in action, but also when at rest, and 

 the points are bent in the same direction in 

 which the currents flow. 



The substance of the cilia is transparent, and 

 for the most part colourless ; in some, however, 

 it is coloured brown or yellowish brown. It 

 appears as if homogeneous, even when highly 

 magnified, and no fibres or globules are distin- 

 guishable in it. It seems to vary somewhat in 

 consistency, for the cilia on some parts appear 

 extremely soft and pliant, and on others com- 

 paratively firm and elastic, though still abun- 

 dantly flexible. 



There is a peculiarity in the form of the cilia 

 in some animals, of which the Beroe and other 



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