DIMENSIONS OF TVENIA SAGINATA. 



429 



posed of 1318 joints. Close behind the head, which has a size of 

 1-7, the neck is 0'8 mm. broad, and at a distance of 5 cm. it has 

 grown to 1*5 mm. The first 6 to 8 mm. are destitute of any clear 

 segmentation, but after that the segments follow each other so closely 

 that 270 can be distinguished within the 5 cm. just referred to. In 

 spite of this very considerable number, the last joints have a length 

 of - 5 mm., which by the end of the second length of 5 cm. (380th 

 joint) has risen to 0'8 mm., with an associated breadth of 3 mm. 

 The next 25 cm. contain fewer joints than did the first 10 viz., 247, 

 of which the last are 1'5 mm. long by 5 mm. broad. Henceforward 

 the size rapidly increases, while the number of joints sinks in pro- 

 portion. Thus, taking successive lengths of 50 cm. each, we have 

 the following results : 



36 85 cm. contained 180 joints, of which the last was 4 mm. long by 10 mm. broad. 



86135 

 136185 

 186235 

 236285 

 286335 

 336385 

 386435 

 436485 



135 

 107 

 91 

 83 

 64 

 53 

 48 

 30 



The last 249 cm. contain not more than 278 joints a marked 

 contrast to the anterior 235 cm. in which there were 1040. The 

 above measurements also show that the greatest breadth occurs about 

 the middle of the body. From that point it decreases both anteriorly 

 and posteriorly, and posteriorly although the length always continues 

 to increase, which is to be regarded rather as the result of an extension 

 than of growth. It is only in the last 100 joints that the length 

 exceeds the breadth. 



When the state of contraction alters, then the relation of length 

 to breadth must also alter. We can best perceive this by direct 

 measurement, such as is again afforded us by a much contracted 

 specimen only 206 cm. long in the Zoological collection at Leipsic. 



The contracted state of this worm is most plainly seen at the neck, 

 which passes anteriorly without any marked decrease in size into 

 the head (which measures about 2 mm.), and at a distance of 6 cm. 

 behind possesses a breadth of 4 mm. The segmentation can be 

 followed almost to the head, although the number of the segments 

 is at first difficult to determine. I do not think, however, that I am 

 far from the true facts of the case when I credit the foremost centi- 

 metre with about 200 segments. The number is greater than that of 

 the succeeding 5 cm., which only exhibit 186. The length of the 

 joints has, however, increased proportionally, rising from O'l mm. at 



