via PRESERVATION AFFINITIES 229 



must be diluted in the proportion of two volumes to three of 

 water. This solution is added cautiously to the capsule in which 

 the Rotifers lie, and they are watched till their ciliary motions 

 slacken ; when this happens a drop or two of osmic acid solution 

 (-J- to 1 per cent) is added ; the Rotifers are then sucked up by a 

 capillary pipette, and transferred to fresh water ; and then into a 

 solution of " Formaline " diluted to contain 2^ per cent of formic 

 aldehyde. In this solution they are transferred to shallow cells, 

 ground out of the centre of an ordinary glass slide, covered with thin 

 glass, and sealed. 1 Other methods of preparing Rotifers for minute 

 study will be found in the papers of Plate, Tessin, and Zelinka. 



The zoological affinities of the Rotifers have long been a 

 subject of keen interest. As early as 1851 Huxley 2 suggested 

 that they represent a primitive form, preserved, with modifica- 

 tions, in the larva of Molluscs, Annelids and other worms, and 

 Echiuoderms. Similar views were later maintained by Lan- 

 kester, 3 who termed the larva of Polychaets, etc., a "trocho- 

 sphere," for which " trochophore " has been substituted in order 

 to avoid confusion with the Rotifer Trochosphaera ; Balfour, 4 

 Hatschek, 5 Kleinenberg, 6 and others have developed these views. 

 Serious difficulties, however, arise in the detailed comparison 

 of Rotifers with this type ; and the special students of this Class 

 have found it practically impossible to agree in the identification 

 of the various parts, a difficulty especially felt in the case of the 

 Rotiferan genus Trochospkaera, though this is just the one which 

 presents the closest superficial resemblance to the Trochophore 

 larva. I have been induced to take a view of the structure of 

 Rotifers that brings it into close relationship with the lower 

 Platyhelminthes, and with the more primitive larva of the 

 Neniertines termed Pilidium (Fig. 60, p. 113). This is hemi- 

 spherical, ciliated all over, with the mouth in a ventral funnel 

 lined by fine cilia ; while the edge is fringed with two rows of 



1 Journ. Quekett Club, set. 2, vol. v. 1892-94, p. 205. 



2 Trans. Micr. Soc. (n.s.) i. 1853, p. 18 (read Dec. 31, 1851): "We may say, 

 therefore, that the Rotifera are organized upon the plan of an Annelid larva. . . . I do 

 not hesitate to draw the conclusion . . . that the Rotifera are the permanent forms 

 of Echinoderm larvae, and hold the same relation to the Echinoderms that the Hydri- 

 form Polypi hold to the Medusae, or that Appendicularia holds to the Ascidians." 



3 Quart. Journ. Micr. Sri. (n.s.) vol. xvii. 1877, p. 399. 

 1 Ibid, (n.s.) vol. xx. 1880, p. 381. 



5 Arb. Z. Inst. Wicn, vols. i. iii. v. 1878-84 ; Lehrbuch der Zoologie, part iii. 1891. 

 8 Zeitschr. wiss. Zool. vol. xliv. 1886, p. 1. 



