148 



THE ROTATORIA. 



^139. 



arc two or three on each side, and sometimes there are from five to eigVit 

 pairs/-' but rarely more/'" 



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

 their canals join in a conunon, 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 a({uiferous 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 i'unction, 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 pai'tly 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.*^' 



'1 Notomwata cope us, and syrinjc. 



3 With Notommata clavulata, and mi/rmeleo, 

 Ihe number of these organs is remarljable ; each 

 lateral band has thirty-six to forty-eiglit ; see 

 Bhrenbers, Die Infusionsthierchen, Taf. XLIX. L. 



4 Ehrenber^ was the first to direct the atten- 

 tion of naturalists to these two lateral bands and 

 their cnntractile vesicles ; but he regarded them 

 as tw.) testicles with their vesiculac seminales 

 (Abhaiidl. d. Berl. Akad. 1830, p. 51). The incor- 

 rectness of this opinion, and which he has main- 

 tained in his grand work, cannot be doubted, if it 

 is considered that these two bands with their 

 appendages are already developed and in activity 

 with the young animals, and this even before they 

 have escai^ed the cavity of the parental body. 



In all Elirenberg''s pubUshed figures, one no- 

 tice.'* nothing of the fie.\uous canals of these or- 

 gans, and which, therefore, he does not appear to 

 liiive observed. 



5 The respiratory orifice is cervical with Entero- 

 plea, Hydatina, Dig/ena, and many species 

 of Notommata; but, with Rotifer, Philodinay 



Brachionus, and some species of Salpina, Euch- 

 lani.t, and Noto7nmata, it is replaced by a tube. 



With Actinurus, exceptionably, a simple res- 

 piratory tube is placed under the throat ; and with 

 Tubicolaria, and Melicerta, there are two in the 

 same region. 



1 Witli Conockilus, and Lacimilaria, where 

 several individuals are attached by their tailu 

 around a common centre, the nucleus of one of 

 these colonies is formed by a loose, gelatinous sub- 

 stance, in the cells of which these animals can par- 

 tially withdraw themselves. With Oecisle.t, Tu- 

 bicolaria, Stcphanoceros, F/oscii/arin,:\nd Lim- 

 iiias, each individual occupies an isnlatcd and 

 more or less hard gelatinous tube {Ehroibrri;, Die 

 Infusionsthierchen). Tlie tubes of Melicrrta, of 

 which Schaffer has given an excellent figure (Die 

 Blumen-polypen der siissen Wasser 1755, Taf. I. 

 II.), are very remarkable, and according io Ehren- 

 berg, are composed of brown polygonal cells which 

 are excreted through the cloacal opening ami 

 glued together (Die Infusionsthierchen, p. 406). 



