718 OCCUERENCE AND DEVELOPMENT OE BOTHKIOCEPHALUS LATDS. 



As found in the pike, the worm is long and narrow, not flat, 

 however, but somewhat round and distended.^ It varies in length 

 from 1 to 2'5 cm., and in breadth from 2 to 3 mm. When much 

 contracted, the body assumes, of course, a more compact form, the 

 longitudinal diameter becoming reduced by more than half, and 

 the thickness increasing in proportion. This is especially seen in 

 front, where the head, as seems always the case in the pike, 

 is invaginated, so that the subsequent external surface is wholly 

 turned inwards, bounding a narrow irregular cavity, which begins 

 with a distinct depression in the middle of the anterior end, 

 and is about 0'5 mm. deep. If the parasites be put into luke-warm 

 water, salt solution, albumen, or gastric juice, and kept at the 

 temperature of an incubating apparatus, the head is usually evaginated. 

 It appears as a more or less club-shaped or glandiform top, hardly 

 1 mm. in length, bearing on each of the sides which correspond to the 

 greater transverse diameter of the body a rather shallow suctorial 

 groove, thus agreeing essentially with the head of the 

 future Bothriocephalus. Like the head end, so also the 

 rounded thin posterior extremity is not unfrequently 

 retracted, though only of course to the extent of a small 

 inconspicuous depression. There is, as we should expect, 

 a priori, no trace of a proper caudal bladder (see p. 377). 

 The body throughout its whole extent is solid, and in 

 structure essentially similar to the adult, biit without 

 reproductive organs, and without segmentation, although 

 transverse wrinkles produce at first sight a similar 

 impression. In comparison with the adult Bothrio- 

 cephalus, the multitude of calcareous corpuscles is very 

 striking ; they are almost uniformly distributed through 

 the body, and in such numbers that the larvEe when fresh 

 appear almost white. In moist warmth the worm makes 

 very energetic movements. Not only is the head 

 repeatedly protruded and retracted, while one wave of 

 contraction after another passes over the body, but the 

 worm bends and straightens alternately like a wliip, and 

 aius '^latus, ^^^ h&a.^ presents many changes in form and general 

 with protru- appearance. 



ded head. ( x „, . 



6.) J-he capsule round the worm is not at aU firm, 



so that not unfrequently, especially on the intestinal 



wall, the worms are seen with one end projecting into the body- 



1 Through the kindness of Prof. Braun, I have been enabled to examine a large 

 number of bladder-worms from the pike, and resulting Bothriocephali of different sizes, 

 for which I feel constrained ^fSJ^^ ^1^J^^^@ 



IfI 



Fig. 378. 

 — Larva of 

 Bothriocephr 



