ON MICROSCOPIC DISCOVERT. 



635 



animalcules whose alimentary structure con- 

 sists of a number of sacs only, and the latter, 

 those which have true alimentary canals and 

 rotatory organs. Of the entire genus, Mr 

 Pritchard remarks, " They are naked, con-' 

 tractile, and possess cilia circularly disposed 

 near the mouth, producing a vortex in the 

 water : in many of them they appear to rotate 

 like a wheel ; to account for which, various 

 hypotheses have been invented. According 

 to Dr Ehrenberg, this is occasioned by their 

 peculiar disposition, and not from any differ- 

 ence of structure ; for as with the vibrating 

 cilia, the base of each is a bulb (similar to the 

 species of the Echines), which by means of 

 muscular fibres it can move in any direction, 

 like a ball and socket joint. Thus each cilium 

 in its revolution describes a cone, the apex 

 of which is the bulb. Now if the cilia are ar 

 ranged in a circle, and viewed laterally while 

 in motion, the whole wheel will appear to re- 

 volve as each ciliurn passes ; first, a little nearer 

 the eye on this side of the cone, and then 

 further off on the other side." 



Plate 35, fig. 57. Vorticella cyathini 

 " This animalcule is shown swimming freely : 

 (he edge of the bell is ciliated, though not ex- 

 hibited in the sketch : it can attach itself by 

 the stem, which it contracts spirally." Its po- 

 lygastric structure is shown in the figure. 



Plate 27, fig. 28. Vorticella anastatica. 

 These polypi form a group resembling a 

 cluster, or more properly an open flower ; this 

 flower or cluster is supported by a stem , which 

 is fixed by its lower extremity to some of the 

 aquatic plants or extraneous bodies that are 

 found in the water ; the upper extremity forms 

 itself into eight or nine lateral branches, per- 

 fectly similar to each other ; these have also 

 subordinate branches, whose collective form 

 much resembles that of a leaf. Every one of 

 these assemblages is composed of one principal 

 branch or nerve, which makes with the main 

 stem of the cluster an angle somewhat greater 

 than a right one ; from both sides of this nerve 

 the smaller lateral branches proceed ; these 

 are shorter the nearer their origin is to the 

 principal branch. At the extremity of the 

 principal branch, and also of the lateral ones, 

 there is a polype or vorticella. There are 

 others on both sides of the lateral twigs, but 

 at different distances from their extremity. 

 These animalcules are all exceedingly small, 

 and of a bell-like figure: near their mouth a 

 quick motion may be discerned, though not 

 with sufficient distinctness to convey an ade- 

 quate idea of its cause ; upon the branches of 

 these clusters are round bodies, which will be 

 more particularly described presently. Every 

 cluster has eight or nine of these branches or 

 leaves; they do not all proceed from the same 

 point, but the points from whence they set out 



are not far asunder ; each of these branches is 

 bent a little inwards, so that all of them taken 

 together form a kind of shallow eup. If the 

 eye be placed right over the base of this cup, 

 the appearance of the whole eight or nine 

 branches is like unto that of a star, with so 

 many rays proceeding from the centre. If 

 the cluster be slightly touched, all the branches 

 instantly fold up, and form a small round 

 mass. The stem which supports the cluster 

 contracts also, at the same time folding up 

 like a workman's measuring rule, that con- 

 sists of three or four joints. This extraordin- 

 ary assemblage constitutes one organized 

 whole, formed of a multitude of similar and 

 also particular ones ; a new species of society, 

 in which all the individuals are members 

 of each other in the strictest sense, and all 

 participate in the same life. 



A few days after one of the clusters is 

 formed, small round bodies or bulbs may be 

 perceived to protrude in several places from 

 the body of the branch ; these grow very last, 

 and arrive at their greatest growth in two or 

 three days. The bulbs detach themselves 

 from the branches out of which they spring, 

 and go away, swimming till they can settle 

 upon some substance which they meet with in 

 the water, and to which they fix themselves 

 by a short pedicle ; the bulbs are then round, 

 only a little flatted on the under side, the pe- 

 dicle continues to lengthen gradually for about 

 twenty-four hours, during the same time the 

 bulbs also change their figure, and become 

 nearly oval. There are in a cluster but few 

 of these bulbs, compared with the number of 

 the vorticellse, neither do all the bulbs come 

 out at the same time. The bulb then divides 

 lengthways into two smaller ones, (see figure) 

 but which are still much larger than the vor- 

 ticellee themselves. It is nor long before these 

 are separated like the first, and thus form four 

 bulbs on the same stalk ; these again diviclo 

 themselves, and form eight; which again sub- 

 divide, and consequently make sixteen. They 

 are all connected with the stalk by a proper 

 pedicle, but they are not all of an equal size ; 

 the largest continue to divide and the smallest 

 begin to open, and take the bell-formed shape. 

 Trembley observed from one round bulb, in 

 about twenty-four hours, by repeated divisions, 

 one hundred and ten vorticellas to be formed. 



Vorticella digitalis. This species of the vor- 

 ticella is very scarce, it seems only to have 

 been seen by Rosel, who found it on the mo- 

 noculus quadricornis, (see figure) till it was 

 discovered in 1 784, by Mu'ller, who had sought 

 for it several years before, but in vain. The 

 body is cylindrical, crystalline, and appears 

 almost empty; it has three pellucid points dis- 

 posed lengthways, the apex is truncated in an 

 oblique direction, the margin bent back. The 



