l5- Prof. KoLLiKER on the Structure of 



penetrates through the muscular envelope of the body into the abdominal 

 cavity. These organs are probably an apparatus for conveying water into 

 the abdominal cavity, resembling that of the Radiata and Mollusca. 



b. Muscular System. 



This system is highly developed ; the suckers and the penis are both fur- 

 nished with muscles, and there is also a peculiar muscular envelope of the 

 body. The latter has a very curious organization : it consists of three lay- 

 ers, the external of which is 0'048 P. L., and the innermost 0*024 P. L. in 

 thickness; both are formed by circular fibres, the former being continuous 

 with the corium, and the latter containing a tubular cavity, through which 

 the intestine passes. The middle layer is formed of longitudinal fibres, which 

 are arranged in such a manner as to form numerous septa or partitions, radi- 

 ating from the centre to the circumference, i. e. from the central to the external 

 layer, thus presenting very much the appearance of a carriage-wheel. There 

 are, moreover, other very short transverse fibres uniting these septa. Con- 

 sequently the entire envelope of the body consists of four distinct species of 

 fibres, very singularly disposed. 



The muscles of the acetabula are the following. Each one is attached to 

 the muscular envelope by two large retractors ; and it has besides a small 

 layer of circular fibres surrounding it externally, and a thick stratum of lon- 

 gitudinal ones internally. 



The penis has a slight layer of transverse as well as longitudinal fibres. 



The muscles seen with the microscope are, like those of the human intestine, 



composed of large flat fibres with nuclei, and neither showing transverse lines, 



nor being united in bundles. 



c. Intestine. 



As far as I could trace the intestine by dissection and with the microscope, 

 it appeared to be very simple. The mouth is placed at the anterior extremity 

 just above the foremost sucker, and is small and elliptic, without any lips or 

 teeth. The intestine itself is a cylindrical tube, which nearly fills the cavity 

 of the body, and runs straight through its whole anterior worm-like part till 

 it reaches the oval sac. Whether it finishes here or not I cannot tell, because, 

 notwithstanding repeated examinations, I was not able to find an anal orifice. 



