1902] The Holothimoiclea of Xortliern Norway. 17 



deeper than usual. Still even in this specimeu. as happ ens so often, 

 single wheels have got free from the snrrounding tissue. so they 

 lie outside the snrface of the body, kept in place by thi^eads of 

 connective tissue. 



Both Théel (1877 and 1886) as well as Leyixsen 11886) look 

 upon Myyiotrochiw riiiku Steexsteup and CJiirodota hrevis Huxlet 

 as the same species. an opinion which nearly all later anthors agree 

 Tvith. As to whether this species has stalked wheels or stalkless 

 ones, these two anthors have different opinions. Théel (1877) 

 conld not discover any vestige of a stalk. He found the wheels 

 he in the most exterior part of the connective tissue. just inside 

 the epidermis. thus enclosed in the skin. Later on. Théel (1886) 

 says that he ..never found stalked wheels. except in speeimens 

 Tvhich were more or less macerated, whereby the Tvheels become 

 free from the surrounding tissue, and bec^^^me attached by their 

 centre to threads of connective tissue." At the same time, Levixsex 

 pronounced a totally different opinion, rå. that the wheels in J/. 

 rinJcii are supplied with a soft stalk, attached to their centres so 

 that they freely reach above the surfaee of the body. He supposes 

 that were the stalks have been overlooked. the reason has been 

 that the T\-heels, by the contraction of the stalks, came to lie in 

 smaU hollows of the skin. Levixsex had then no knowledge of 

 Théel "s later statements. 



My opinion on this matter is in the main the same as Théel's. 

 The skin gets macerated in speeimens ^vhich are laid hito bad Tvater 

 (the surfaee water is often too little salt at the places where this 

 species hves), and becomes macerated even in preserved speeimens, 

 when these are kept in weak alcohol. Through maceration the 

 Wheels become exposed. Every wheel is then kept in its place by 

 the thi^eads attached to its centre, which threads thus assume the 

 appearance of a soft stalk. If there is cousiderable maceration, 

 the Wheels can be seen hanging outside the body, by the naked eye; 

 in less macerated speeimens, by the help of the microscope it will 

 be found, as Levixsex says. that they can be hfted a little above 

 the le vel of the skin with a pencil or a pin. In liding or well 

 preserved speeimens, however, at least the majority of the wheels 

 he embedded in the skin, so that they cannot be moved, except in 

 connection with the surrounding tissue. It is ti'ue that I do come 

 across single exposed wheels even in the best preserved specunens: 



