190 



INVERTEBRATE MORPHOLOGY. 



M 



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

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

 being entirely wanting (Asplanclma). 



The body, with the exception of the anterior portion or 

 trochal disk, Avhich 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 withdrawn, and frequently pre- 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 



GJ or prolongations into spines. 

 A few forms (Floscularia) se- 

 crete a gelatinous case within 



Q V which the}' 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- 

 FIG. 93. Brachionus urceolaris (after 



ECKSTEIN*. 



Br = nerve-ganglion. 

 cv contractile vesicle. 

 Gl = digestive glaud. 

 M = muscle. 

 Met = mastax. 

 N nephridial canal. 

 = eye. 

 Oc = ocellus. 



Ov = ovary. 

 Sp = calcar. 



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 

 bauds of cilia Avhich follow the 

 lobations, when two bands are 



present one being entirely 

 prseoral 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 pmeoral, being some- 



