32 ILLINOIS BIOLOGICAL MONOGRAPHS [32 



Of a somewhat more limited distribution is the oral armature of spines 

 in the schistosomatid C. gracillima (Fig. 142) . These spines are turned into the 

 body with the inpocketing of the oral sucker-pouch, so that the animal in the 

 condition of contraction appears perfectly aspinose except for the armature 

 of the acetabulum. But with its protrusion the oral sucker is crowned with 

 a sohd cap of spines. 



The hood of spines of the echinostome group is specialized and valuable 

 in systematic work. It is usually an incomplete ring, consisting of a circlet 

 of spines around the dorsal side, extending ventrad into the middle half of 

 the body. Dietz (1910) has sketched 63 figures of spine characters and 

 numbers in his monograph on the Echinostomidae of birds. The adult echi- 

 nostomes of North America have received little attention and in consequence 

 of the difficulty in working out the exact spine number in the larva a descrip- 

 tion of the specific spine characters of the cercariae will not be worth while 

 until more attention is given to the adults of the family. 



The stylet is the unique larval organ in the group of the xiphidiocercariae. 

 It might be more properly called a quill than a stylet, for its value as an organ 

 of piercing is questionable on account of its frailty and frequently disadvanta- 

 geous leverage. It is a mucoid structure, situated in the dorsal wall of the oral 

 pocket, well supplied with muscles to work it in any direction anteriad and 

 laterad. It is fully formed only in the mature cercaria, and is carried into 

 the cyst (Figs. 84, 85). Quite generally the stylet is recognized as of specific 

 systematic value, and is therefore figured in systematic descriptions (Liihe, 

 1909:189-200), but the stylets as they are figured are so generalized as to be 

 of little value in the identification of species. The stylet is of specific value, 

 but this value lies in the details of the organ rather than in the general out- 

 line. (See Figs. 57, 61, 77, 83, 91, 102). 



The stylet is usually a weak organ mechanically and poorly levered. 

 However, it is resistent to chemicals and indifferent to dyes. The stylet of 

 Cercaria glandulosa is extremely delicate, so that it goes to pieces immediately 

 when a cover glass is pressed down on a water-mount of the worm. The 

 stylet, as a rule, is hard to observe in preserved mounts. 



GLANDS OF THE LARVAL TREMATODE 



Glandular organs in the trematode may be distinguished as dermal, salivary, 

 mucin, cystogenous, genital, and locomotor. The dermal glands are those 

 imbedded in the subdermal tissues, are unicellular, usually flask-shaped, and 

 have a small duct opening to the exterior. The saUvary glands include all of 

 the unicellular glands which open into the digestive tube. Mucin glands are 

 paired, right and left groups of one to several gland cells emptying into the 

 oral pocket thru long attenuate ducts. Since mucin is a constituent of salivary 

 glands, these glands are modified salivary glands. Cystogenous glands are 

 imbedded in the parenchyma and are usually filled with rhabditiform granules 

 which superficially resemble the dermal rhabdites of the Turbellaria but are 



