[33] ENTOZOA OF MARINE FISHES OF NEW ENGLAND. 485 



or rather widening, is more pronounced, and there is the beginning of an 

 independent alar margin. On the next segment the alary margin is one- 

 fourth the breadth of the segment itself, and from it springs the second- 

 ary series of segments. The breadth of the three segments mentioned 

 is 0.82 mm , 0.86 mm , 0.90 mm , respectively, or of the latter, exclusive of the 

 alary, margin, 0.72 mm . The breadth of the succeeding segment is 0.72 mm . 

 The length of each of these segments is 0.26 mm . Length of secondary 

 strobile, 2.46 mm ; number of segments, 21; breadth, 0.20 mm to 0.24 mm ; 

 average length, 0.12 mm . 



Ecersion and inversion of proboscis. — The proboscides do not play 

 backwards and forwards in their sheaths like a piston-rod in its barrel, 

 but each folds in upon itself from the outer extremity like the finger of 

 a glove. When a proboscis is fully extended it has the appearance of 

 a slender, solid cylinder, covered with recurved hooks. If, however, 

 one which is not fully extended be examined, it will be found to be 

 folded in upon itself from the outer end. As the hooks point backwards 

 when the proboscis is extended, it can be easily seen that it is impossi- 

 ble to retract that organ by pulling it in bodily. When the proboscis 

 is entirely retracted it forms a hollow tube, whose outer covering is the 

 inside wall of the extended proboscis, and whose inner coat carries the 

 hooks which now point forward. The whole tube lies in the proboscis 

 sheath. 



The manner of everting and inverting the proboscis seems to be iden- 

 tical in all the Trypaiiorhynchi, both in the mature and later larval 

 stages. The contractile bulbs and proboscis sheaths contain a trans- 

 parent liquid, in which float a few granules. The contractile bulbs act 

 on the contained fluid exactly as the bulb of a syringe. The thick walls 

 of the bulbs are composed of diagonal, interlacing fibers, whose con- 

 traction compresses the bulb and forces the fluid out into the proboscis 

 sheath. The result of this action is to make the proboscis begin to 

 unroll from the anterior end of the sheath. This will continue as long 

 as the walls of the contractile bulbs continue to exert pressure on the 

 fluid contents, or until the proboscis is entirely everted. When the 

 proboscis is fully extended the granular liquid can be seen filling the 

 interior of both proboscis sheath and proboscis. To the interior of the 

 proboscis, at the anterior end, is attached a tubular cord of very con- 

 tractile tissue, which lies in the hollow of the proboscis, extends back 

 through the sheath, and is inserted at one side on the inner wall of the con- 

 tractile bulb. The proboscis is inverted by the contraction of this cord. 

 When the proboscis is inverted this cord lies in kinks and irregular coils 

 in the contractile bulb and posterior end of the sheath. This move- 

 ment is made rather quickly by the living worm. Upon removing some 

 Specimens from the pylorus of a Dusky Shark, it was noticed that when 

 the heads were touched by the point of a scalpel or needle, even when 

 the head was partly imbedded in the mucous membrane, the probos- 

 cides would be suddenly retracted and the worm detached. 



