190 



INVEBTEBRATB MOEPEOLOQT. 



Oc 



having in such cases the form of a sucker (Philodina), or ter- 

 minating in two movable lamellae, Brachionus (Fig. 93), or else 

 being entirely wanting (Asplanchna). 



The body, with the exception of the anterior portion or 

 trochal disk, which bears the bands of cilia, is enclosed in a 



chitinous cuticle, occasionally 

 comparatively thick and firm, 

 forming a case, the lorica, into 

 which the softer parts may be 

 withdrawn, and frequently pre- 

 senting a delicate sculpturing 

 or prolongations into spines. 

 A few forms {Floscularia) se- 

 crete a gelatinous case within 

 Oy which they live, foreign parti- 

 cles being sometimes added 

 to the secretion ; a species of 

 Melicerta, for instance, building 

 a case for itself of pellets man- 

 ufactured from foreign bodies 

 and arranged in oblique or 

 spiral rows and cemented to- 

 gether by the gelatinous secre- 

 tion. 



„.,„,• , . The trochal disk which oc- 



9o. — Brachwnus urceolans (after ■ ,i , . 



cupies the anterior end of the 



body is but rarely circular in 



outline ; more usually it is 



lobed at its margins and may 



even be separated into two 



parts. The margin of the disk 



is .surrounded by one or two 



bands of cilia which follow the 



lobations, when two bands are 



present one being entirely 



prsBoral and the other postoral in its position, so that the 



mouth lies between the two on the ventral side of the disk 



Various differences of arrangement of the bands are found 



in different species, one of them, the prseoral, being some- 



FlG 



Eckstein). 

 Br = nerve-gangliou. 



ev = coutiactile vesicle. 

 01 = digestive gland. 



M = muscle. 

 Ma = mastax. 



N = nephridial canal. 



= eye. 

 Oe = ocellus. 

 Ov = ovary. 

 Sp = calcar. 



