INFTTSOEIAI ANIMALCULES. 79 



the vaginal canal. It is exceedingly delicate, and may be seen to 

 conti'act, by the action of muscular fibres, with great rapidity, in 

 which act it is thrown into numerous regular folds or pouches, and 

 in that condition appears not very dissimilai' to the large cellular 



lungs of Batrachia The explanation which I ventui-e to 



give, is, that this sac draws in water and expels it again by the 

 vaginal orifi.ce ; and it is by bringing the blood, by means of the 

 ciliary movements of the tags, into intermediate contact — (the 

 delicate membranous wall of the sac intervening) with the air of 

 the water, that aeration or respiration is performed. An analogous 

 contractile sac may be seen in Rotifer vulgaris y 



Elirenberg described the several organs discussed, assuming the 

 existence of a respiratorj^ apparatus, evidenced in the tremulous tags, 

 and which ho designated gill-like organs, or gills. His views are 

 represented by the following abstract : " Oval tremulous bodies are in 

 some species, observed attached to a free filament-Hke tube, generally 

 placed longitudinally within the body, (fig. 416) ; in some instances, 

 they are attached to the two sexual glands, as in Hydatina. Their func- 

 tion is respii'atory, and they are analagous to gills ; the tremulous 

 motion observable, being that of the lamina composing them. The 

 reception of water within the body, for these organs to act upon, is 

 provided for, by one or more openings at the anterior part of the 

 body, furnished, in some species, by spur-like processes, or tubes," 



The aimular cords, producing the semblance of articulations in the 

 body of many Rotatoria, were surmised by Ehrenberg to be vessels, 

 but, as before stated, the general opinion is that they are muscular. 

 In some examples, he also described the vessels to form a net- work, 

 more or less distinct, below the margin of the mouth, and connected 

 by free longitudinal cords to the interior sxxrface of the body. (pi. 

 ix. fig. 419). 



No naturalist has yet confirmed such a vascular network, as is thus 

 figured and described ; but various delicate muscular threads are 

 known to cross one another, about the neck of these animals, as they 

 pass to theii' insertions in the muscular cushions forming the rotary 

 apparatus. Thus, Mr. Gosse says : " thi-eads with biftu-cate extreme- 

 ties go from the centre of the head to each cone-top (of the rotary 

 organ), each lateral eye, and each antenna." Dr. Dobie also speaks 



