ASPLANCHNA EBBESBORNII (ROTIFER) 415 



Sense organs: The antennae are tubular outgrowths of the 

 ectoderm with number of sense hairs projecting from the apex 

 of each. In their early development, these hairs show a slight 

 vibratory action, but when fully developed they are stiffer and 

 firmer and serve as organs of touch. Delicate nerves extend 

 from the brain to the different antennae. There are four an- 

 tennae present, two at the anterior end and one on either side 

 of the body in a dorsolateral position, nearer the posterior end 

 (figs. 1 to 3, and 6). 



POSITION OF ROTIFERS IN THE ANIMAL KINGDOM 



The position of rotifers has been a subject of considerable 

 controversy. Huxley ('51) suggested that they represent a 

 primitive form and are preserved, with modification, in the 

 larvae of molluscs, annelids, and other forms. Lankester main- 

 tained a similar view and considered the trochophore of worms 

 and molluscs, when compared with rotifers, as possessing close 

 relationships. Hartog held the view that the structure of the 

 rotifers brings them into close relationship with the lower flat 

 worms and with the more primitive larvae of the Nemerteans, 

 the Pilidium, and that there is a striking resemblance in the 

 structure and function of the different parts, when carefully 

 compared. Thus the rotifers, he says, may be considered as a 

 group apart, but probably representing an early offshoot from a 

 free-swimming plathelminths (Rhabdocoele) with minor change. 



Zelinka endeavored to prove that the course of development 

 in the rotifer Callidina russeola, as well as other rotifers, shows 

 affinites with the trochophore larvae of Annelida and Mollusca, 

 and that the adult rotifers are in a sense persistent trochophore 

 larvae. Balfour states that the trochophore larva is found in 

 rotifers where it is preserved in the adult state, and that there 

 is every reason to believe that the types with trochophore 

 larvae, viz., the Rotifera, the Mollusca, the Chaetopoda, and 

 the Polyzoa, are descended from a common ancestral form, and 

 that it is also fairly certain there was a remote ancestor common 

 to these forms and to the Plathelminthes. Other investigators 



