148 THE ROTATORIA. § 139. 



are two or three on each side, and sometimes there ire from five to eight 

 pairs/"' but rarely more.® 



The lateral bands approach each other at the posterior extremity, and 

 their canals join in a common, highly-contractile vesicle with thin walls, 

 which empties externally its aqueous contents through the cloacal open- 

 ing.'^' 



An orifice, situated usually upon the neck, and sometimes pedunculated, 

 serves probably to introduce the water into the cavity of the body. This 

 water enters the aquiferous system through the lateral vessels which float 

 free in this cavity, and at last is expelled through the contractile vesicle. 

 In this way, a constant renewal of water can occur, and the opening upon 

 the neck may therefore be properly termed a respiratory orifice or tube.^'^ 



There can be but little doubt that the rotatory organs also, have a respir- 

 atory function, for their surface is covered with thin epithelium, and their 

 cilia produce a constant change of the water. 



CHAPTER VIII, 



ORGANS OF SECRETION. 



§ 139. 



Some of the Rotatoria secrete a gelatinous substance, which, hardening, 

 forms the cells and tubes into which they can partly or wholly withdraw 

 themselves. The organ of this secretion is yet unknown; but the secretion 

 appears to be derived from the posterior extremity, and especially from the 

 cloacal opening. '^^ 



2 Notommntn enpeus, and syrinx. Brnchionust, and some species of Salpina, Ench- 



3 With Notommata clavitlata, and myrmeleo, laiiis, and Notormnata, it is replaced by a tube, 

 the number of tliese organs is remarljable ; each With Actinnrus, exceptionably, a simple res- 

 lateral band has thirty-six to forty-eight ; see piratory tube is placed under the throat ; and,with 

 Ehrenbers, Die Infusionsthierchen, Taf. XLIX. L. Tubiro/aria, and Melicerta, there are two in the- 



■4 Ehrenber^ was the first to direct the atten- same region, 



tion of naturalists to these two lateral bands and 1 With Conochilus, and iMcinularia., where 



their contractile vesicles ; but he regarded them several individuals are attached by their tails 



as two testicles with their vesiculae seminales around a common centre, the nucleus of one of 



(Abhandl. d. Berl. Akad. 1830, p. 51). The incur- these colonies is formed by a loose, gelatinous sub- 



rectness of this opinion, and which he has main- stMiirr, in tli^' I'ells of which thfsc animals can par- 



tained in his grand work, cannot be doubted, if it tially uithilriiw themselves. Willi Oii-islcx, Tu 



is considered that these two bands with their bira/tiriii, Uli plianoceros, F/(>Krti/iiri((, ;ind Liin 



appendages are already developed and in activity nia^, each individual occupies an isolated anil 



with the young animals, and this even before they more or less hard gelatinous tube (Elirenber!^, Die 



have escaped the cavity of the parental body. Infusionsthierchen). The tubes of Melicerta, o{ 



In all Ehrenberi^'x published figures, one no- which Schaffer has given an excellent figure (Die 



tices nothing of the flexuous canals of these or- Blumen-polypen der süssen Wasser 1755, Taf. I. 



pans, and which, therefore, he does not appear to II.), are very remarkable, and according to Ehren- 



have observed. berg, are cunipnsed of bmwu imlygonal cells which 



5 The respiratory orifice is cervical with Bwtero- are excreti-d tlirough the elnac;d oi>ening ami 



plea, Hydulinn, Diglena, and many species glued together (Die Infusionsthierchen, p. 406). 

 of JSuluininata; but, with Rotifer, Plii/odina, 



