Phylogeny of Animals 531 



taceans, and of many adult ones. We would suggest that 

 the complete evolutionary history of these starts with some 

 of the Rotifera, and is carried up unbroken through the Crus- 

 tacea to still higher arthropods. As is now well recognized 

 the larval nauplius and zosea stages of Crustacea show some- 

 times two, usually three, occasionally four pairs of setaceous 

 appendages, the antennae, antennules, mandibles, and maxillae. 

 These act at once as feelers, propellors, and accessory mouth 

 appendages. All of them, in varying degrees of development, 

 or of dorsal and ventral paired fusion, can be traced in Roti- 

 fera. Unfortunately, where almost certainly fusion occurs, 

 we as yet have little exact knowledge as to double nerve supply, 

 or indications of nerve fusion. 



In not a few genera of Rotifera the trochal disk, with its 

 cilia or ciliary circlets or tufts, constitutes the only motile 

 and directive structure. Many of the loricate genera exhibit 

 this, also Lacimilaria, Megalotrocha, and others. But in Scar- 

 idium two dorsal outgrowths of the disk that have been de- 

 scribed as "rocket-headed antennae" appear as slight swell- 

 ings. These again, as Floscularia mentioned below indicates, 

 may fuse to form a single short dorsal movable process, usually 

 with setae, as in Brachionus, or a long flexible appendage with 

 terminal setae as in Cephalosiphon and Rotifer. 



But below and in front of, or more ventrally than the above, 

 two other appendages may arise as setigerous papillae or knobs 

 or elongated and highly flexible organs. In this connection 

 CEcistes is noteworthy. In CEcistes serpentinus the dorsal 

 organs appear only as two hooked processes adnate at the 

 base, the ventral organs as two minute papillae. But in other 

 species the latter may become elongated and conspicuous, 

 while "they move independently of each other but not spas- 

 modically." 



In Floscularia the species F. Hoodii has two evident dorsal 

 appendages, and two small setaceous latero-ventrals, while in 

 other species the dorsal ones are evidently fused into a long 

 median dorsal process. In Melicerta the latero-ventrals are 

 long supple setigerous appendages, while the two dorsals seem 

 to have fused into a small dorsal setigerous papilla. In As- 

 planchna Ebbesbornii "there is a rectangular nervous ganglion 

 just under the corona," and a nerve thread passes from each 

 corner of the ganglion to two dorsal setaceous swelHngs, and 

 two lower latero-ventrals. But, further, just below tlie latter 

 and above the mouth two added appendages appear with nerve 

 supply from the latero-ventrals. The same is seen in A. prio- 

 donta. 



