430 GROWTH AND STRUCTURE OF TCENIA SAGINATA. 



the beginning of this series of joints to 0'5 mm. at the end. Twenty- 

 five cm. further back, and therefore at a distance of 31 cm. behind 

 the head, the breadth of the body has increased to about 10 mm. 

 There were 376 joints in this length, but the greater part of these 

 were in the anterior 12 cm., for the length of the joints increases 

 posteriorly very nearly up to 2*6 mm. The remaining 150 cm. were 

 composed of 321 segments, of which the three successive lengths of 50 

 cm. contained 170, 91, and 63 respectively. The length and breadth 

 of the last segment of each division were expressed by the following 

 ratios: 4-3 : 11-5, 7 : 11, 12 : 6-5. 



The total number of segments in this worm was about 1083, but 

 it is not perfect, having lost its posterior end, perhaps in connection 

 with the strong contraction which it has undergone. A comparison 

 with the worm first measured would lead us to conjecture that this 

 end measured about 200 cm., and was composed of perhaps 200 

 proglottides, so that we may fairly attribute to this animal a length 

 of about 400 cm., and about 1300 joints. 



Earlier computations all fall short of this result. In the first 

 edition of this work, at a time when I had seen no perfect specimen 

 (with the head), I estimated the number at about 1000. Dr. A. 

 Schmidt in Frankfort counted on a worm of " not very great size " 

 1058 joints, including 100 ripe proglottides, and Sommer, who has 

 most intimately examined the Tcenia saginata, fixes the number at 

 1221. The differences seem more considerable than they are in 

 reality, for they result simply from the circumstances that the anterior 

 segments, which can only be made out with difficulty even with the 

 microscope, have been left out of account, and that the computation 

 has in fact begun at a varying distance behind the head. 1 But a 

 single centimetre sometimes makes a difference of more than a hundred 

 joints. And since neither Schmidt nor Sommer have given any de- 

 tailed report as to the nature of their " first " joint, I think we may 

 assume that the most anterior portion has been left out of account. 

 An absolutely correct computation is thus impossible, for the segmen- 

 tation begins so gradually that the determination of the first joint is 

 an exceedingly doubtful matter. 



The boundaries of the individual joints are marked at first by 

 simple furrows. These, though at first but shallow (Fig. 244), after- 

 wards become somewhat deep, and are not exactly perpendicular to 

 the long axis of the worm, but rather inclined forwards at an acute 

 angle, so that the posterior border of one segment overlaps the 

 beginning of its successor like a cuff. The arrangement may indeed 



1 Kuchenmeister in his first work (p. 112) describes the foremost joint of his Tcenia 

 mediocandlata as 1 mm. long by 3 broad. 



