'OG SYSTEMATIC HISTORY OF THE INFUSORIA. 



FAMILY VIII.— BEACHI0:N^/EA. 



The concluding family of the Rotatoria, Brachion^a, is distinguished by 

 its members having two rotai7 organs and a lorica. 



The lorica is open at the extremities, like a tortoise's carapace. The rotary 

 apparatus is often apparently composed of five parts, three central and two 

 lateral ; of which the latter alone belong actually to it, the others being only 

 ciliated frontal portions, which during the vibration of the trochal disc remain 

 stiffly extended as feelers. Besides these appendages, the disc presents in 

 most, perhaps in all the species, two setae, as is seen also in Synchceta. The 

 genera Noteus and Brachionus have a forked foot, Anurtea is destitute of 

 feet ; and Pterodina has a suctorial disc at the end of the foot, but no toes. 

 All the genera have jaws, with teeth attached to an oesophageal head, having 

 four muscles. In Pterodina the jaws are partly two-toothed and the teeth in 

 a line (zygogomj^hia, lochogomphia), in the other genera they are many- toothed 

 {fohjgompMa). In Noteus and Pterodina, the alimentary canal is constricted, 

 forming stomachs (gasterodela) ; in the rest it is partly simple {ccelogastrica), 

 partly with stomachs. Glands have been observed in aU the genera, as also 

 an ovary and contractile vesicle. Many species of Anurcea, Brachionus, and 

 Noteus, carry their eggs attached to them, after expulsion. In aU the genera, 

 except Pterodina, internal tremulous tags attached to the water-vascular 

 canals have been observed. A nervous system is supposed to be indicated by 

 the presence of red visual points in aU, except Noteus, which, however, 

 possesses what is believed to be a cerebral ganglion. 



Some of the Brachionaea may become so numerous as to render the water 

 milky and turbid. 



Ehrenberg's classification of this family is given at p. 479. 



It was amongst the Brachionaea that some of the most interesting of recent 

 investigations were first made by Perty, Cohn, and Leydig. Thus, striped or 

 voluntary muscles have been noticed in Brachionus militaris by Cohn, and in 

 Pterodina by Leydig ; whilst, in the latter case, the same distinguished 

 observer alleges that he finds a refracting body in the eye similar to what he 

 had detected in Eucldanis and Stephanops. In Brctchionus urceolaris and 

 militans, again, Perty and Cohn have established the existence of dioecious 

 sexuality amongst the Rotatoria — the male animal, as in the previously de- 

 scribed dioecious forms, being devoid of an alimentary canal ; and to this list 

 Mr. Gosse has since added B. Pala, B. ruhens, B. ampMceras, B. angidaris, 

 B. Dorcas, and B. Mulleri. Its rarity, and the comparatively short period of 

 time during which, according to Perty, the male animalcule of Brachionus 

 urceolaris exists, probably explain why these creatm^es have been so long over- 

 looked. Cohn observed that the contractions and expansions of the contrac- 

 tile sac at the base of the water- vascular canals of Brachionus militaris were 

 accompanied by a corresponding motion in their watery contents. At each 

 contraction, or systole, a stream was expelled into the cloaca, communicating 

 with the water in which the creature lived, whilst an opposite movement 

 attended the expansion or diastole of the sac. These facts strongly corro- 

 borate the supposition that the water-vascular canals are the true respiratory 

 organs of the Rotifera, corresponding with the remarkable analogous organs 

 arising from the cloaca of the Holothunm amongst the radiated animals ; the 

 pure oxygenated water being thus carried to the fiuid distending the body, 

 which fulfils the functions of the blood in higher animals, and affording an 

 example of the " Phlebenterism" of the French naturalist Quatrefages. 



In Brachionus militaris, Cohn has also pointed out the existence of three 



