308 LEIDY'S DESCRIPTIONS OF DISTOMA. 



vibrillse continues even after the vessel is torn into small fragments, but gradually 

 becomes slower and slower until it finally ceases When in full activity it 

 resembles a rapid succession of waves crossing each other, (fig. 11, a.) as it 

 becomes slower the crossing appearance ceases, (d.) it then appears as a spiral, 

 {b.) and lastly as one wave slowly falling upon the other, (c.) In one instance I 

 saw a corpuscle at the commencement of the vessel rapidly driven round in a circle 

 (fig. 10,) through the agency of the vibrillse. Besides this new source of circulatory 

 movement, all the vessels have the power of contracting, even to such a degree as to 

 become totally invisible. After this stage it is probable that this Distoma finishes 

 its development in some other animal, or possibly as an ectozoon. 



Intimate structure. — The body is invested with a very delicate transparent 

 epidermoid membrane, beneath which are observable transverse muscular bands, and 

 as the animal shortens as well as contracts and elongates, we would almost infer the 

 existence of longitudinal muscular bands. The latter, however, do not exist, and the 

 shortening is produced by the same bands which produce the elongation. This 

 appears at first thought almost impossible, but the arrangement of the muscular 

 bands is peculiar, very remarkable, and renders the two opposite movements perfectly 

 easy by the same set. Instead of being continuous bands, they are isolated muscular 

 or sarcous cells arranged in rows and separated by narrow intervals, which from their 

 inherent power of shortening and lengthening in any direction will give the body a 

 resultant movement. This arrangement and change will be better understood upon 

 referring to figure 12. When the sarcous cells are extended transversely to their 

 greatest extent, the body appears broadest. As these shorten, the body is narrowed 

 and somewhat elongated. When they reach their greatest degree of contraction 

 they then elongate in the direction of the length of the animal, and the elongation 

 of the body corresponds to the extent to which the sarcous cells are capable of 

 extending in that direction. These cells appear homogeneous, opalescent, and 

 translucent. 



Within the muscular layer and forming the general parenchyma of the body 

 is a fine, transparent, vesicular structure. These vesicles are very delicate, contain 

 no nuclei, and measure from l-12,500th in. to l-3570ch in. in diameter; some I 

 measured as large as l-1850th in. These same bodies either fill up the interspaces 

 between the viscera in the visceral cavity, or else they form a layer upon the 

 interior parieties of that cavity, a point I could not determine. 



The acetabula are hollow globular bodies with thick muscular parietes, the 

 latter character being distinguished by the striation and inherent contractility. 



The mouth is a sort of shallow canal, formed by the thickness of the parietes 

 of the oral acetabulum. Both orifices of this oral canal are capable of contracting 



