Anatomical structure of Aspidogaster conchicola. 499 



change of position of the long epithelium cells. Osmic acid fluids leave 

 the large globules in the free ends of these latter black which, however, 

 changes when mounted. This may also be taken to indicate their 

 fatty nature. 



Grlands. 



Skin glands. The observer soon recognizes in living Aspido- 

 gasters beautifully glistening outstretched tubes filled with a granular 

 refracting mass. In shape (Fig. 20) they may vary widely, being 

 sometimes short and flask- shaped or more or less curved and like 

 a retort with long neck and large bulb. Sometimes they are ex- 

 ceedingly long and regular, or irregularly thickened, beaded, or wavy. 

 The motions of the animal under pressure greatly modify the shape 

 of these structures and often for some distance they can not be traced 

 until a change in position again permits their granular contents to 

 flow into the constricted parts. 



These are the skin glands and are unicellular. They possess each 

 a nucleus but it can not always be seen on account of the non- 

 transparency of their contents. It is situated in the bulb of the 

 simplest forms and in one of the thickenings of the beaded forms, 

 generally towards the free end, and frequently also pressed to one 

 side, as I have found in sections. I have many a time traced them 

 to their openings through the cuticle which make little depressions 

 from the outside. As indicated above, this is only satisfactorily done 

 where the neck is distended with secretion. Shortly after the animal 

 is mounted this is frequently the case and even large drops of the 

 secretion are found outside of the cuticle at the mouth of the gland. 

 The shining particles of the secretion itself present a lively proto- 

 plasmic motion and soon the whole mass is disintegrated and dispersed. 



In describing the cuticle I have already mentioned globular or 

 elliptical structures of homogeneous apparence bulging out the cuti- 

 cular surface. These I am satisfied are only globules of secretion 

 stopped in the ends of the ducts of skin glands. I have, by taking 

 account of their shape, position, staining, structure and distribution, 

 and by comparison with sections that fall through the ducts length- 

 wise, been able to satisfactorily account for their presence. I am not 

 sure that the skin glands possess a permanent opening through the 

 cuticle. It seems probable that in many cases, during a temporary 

 cessation of function on the part of certain glands, or after a dis- 

 charge of their secretion, a sufficient space of time may elapse for 



