BKACHIONUS UKCEOLAKIS. 



433 



which the transition from the ARTICTJLATA to the MOLLUSCA is accom- 

 plished : the transparent cell, and ciliated tentacula aronnd the mouth, 

 would indicate this creature to be a BKYOZOOJT, to be described hereafter ; 

 but the tentacula are visibly stunted and thickened at their base, thus 

 approximating in character to the cilia-bearing lobes of a Eotifer, while 

 the internal organs (the pharynx, gizzard, and stomach) conform exactly 

 to the type of structure common to the Rotifera. 



(1120.) The body of the Wheel- Animalcules is enclosed in a delicate 

 transparent envelope of con- 

 siderable consistency, often 

 terminating at the upper ex- 

 tremity in wavy indentations 

 and tooth-like processes, as in 

 Bracliionus urceolaris (fig. 

 225, c c). This harder inte- 

 gument is so constructed as to 

 allow the animals to move at 

 large in the element they in- 

 habit. Continuous with the 

 free margin of the shell is a 

 delicate membrane connecting 

 it with the bases of the cilia- 

 bearing lobes around the 

 mouth, so as to allow those 

 organs, when not in use, to be 

 retracted within the cell. 



(1121.) To the posterior 

 extremity of the body is gene- 

 rally appended a pair of for- 

 ceps, composed of two move- 

 able pieces (figs. 225 & 230), 

 used as anchors, or instruments 

 of prehension ; and by means 

 of these the little creatures 

 fix themselves to the Confervaa 

 or aquatic plants amongst 

 which they are usually found. 

 In Brachionus urceolaris the prehensile forceps (fig. 225, j>,)t is attached 

 to the extremity of a long flexible tail (o), wherein the muscular fibres 

 destined for its motions are distinctly visible. 



(1122.) The cilia, whose action produces the appearance of wheels 

 turning upon the anterior part of the body ; are variously disposed ; and 

 from their arrangement Ehrenberg * has derived the characters whereon 



* Abhandlungen der Koniglichen Akademie der Wissenschaften zu Berlin for 

 1833. 



2F 



Brachionus urceolaris (after Ehrenberg) : o, b, c, 

 rotatory apparatus and marginal teeth of the shell ; 

 d, " calcar," or tubular prolongation of the shell, 

 communicating with the visceral cavity; e, oculi- 

 form spot ; f, gizzard with its enclosed masticatory 

 apparatus ; g, stomachal cavity; h h, caecal append- 

 ages to the stomach; k, common outlet; I, lateral 

 canals, to which the vibratory organs are attached 

 in, contractile vesicle ; , ovaries ; o, flexible tail, in 

 which the muscular bands are distinguishable; p, 

 terminal forceps. 



