PECULIARITIES OF YOUNG SPECIMENS. 



743 



of 23 mm. from the posterior end of the body, an annular constriction 

 was evident, 1*5 mm. deep at one lateral margin, and 1 mm. at the 

 other, and separating off the last seventeen joints. A second con- 

 striction occurred 17 mm. further up, isolating an almost equal 

 number of joints (fifteen), but less deep than the one behind. 



I do not think I am wrong in regarding these grooves as the first 

 signs of the commencing separation, and am confirmed in this opinion 

 by the fact that they do not coincide with the boundaries of two 

 joints, but extend across the surface of a joint. Since the end of the 

 chain exhibited only half a joint with a cirrhus-pouch, my supposi- 

 tion seems fully justified. 



Among the specimens of Bothriocephalus cordatus, there were, 

 besides adult chains of joints, several young 

 worms, which were of special interest on 

 account of several peculiarities, which have 

 not, so far as I know, been elsewhere observed 

 in young Bothriocephali. It was even possible 

 to form a tolerably complete series of such 

 forms, and thus to elucidate in an unex- 

 pected manner the early stages of the species. 



The smallest of these young worms 

 measured not more than 30 mm. It ex- 

 hibited, like the others, a clear, almost 

 transparent appearance, due not only to the 

 absence of cortical granules, but especially 

 to the thinness of the body and the 

 slight development of the muscles. The 

 greatest breadth (3 mm.) was exhibited a 

 short distance behind the head. The anterior 

 end already showed the characteristics noted 

 in the adult. The posterior third of the 

 body was, however, strikingly different, be- 

 coming gradually narrower, and ending in a 

 thin point. The head exhibited the adult 

 form, but was of much smaller size (0'8 mm.), 

 while the body was divided into about 140 

 narrow segments, of which those about the 

 middle were not only the broadest, but also 

 the longest. 



The other worms exhibited a 

 structure, and measured from 40 to 100 mm., increasing gradually in 

 breadth to 5 '5 mm. Not only did these larger specimens resemble 

 the smaller in form, but even in the number of segments, which 



FIG. 401. Four young 

 specimens of Bothriocephalus 

 similar cordatus (nat. size). 



