SCOLEX, STROBILE, PRO GLOTTIS. 137 



or caudal, segment is always the oldest, the newly-formed segments 

 continually pushing the others from before backwards. 



(353.) Most frequently the mature segment QT Proglottis is detached, 

 as stated above, and becomes an independent worm : nevertheless this 

 probably does not invariably happen, some apparently remaining per- 

 manently connected together, and laying their eggs without having 

 enjoyed a separate existence, as is the case in various forms of Asci- 

 dians and Polyps. 



(354.) While the segments of the Strobile remain conjoined, they 

 seem to enjoy a complete community of life and of movement. Some 

 species especially may be observed to become suddenly dilated in one 

 region and contracted in another these alternate movements, passing 

 along the entire length of the animal, giving precisely the same ap- 

 pearance as is witnessed in many Annelidans when they make violent 

 efforts for progression, a circumstance which will readily explain how 

 Taenia3 are frequently met with having their bodies tied in complicated 

 knots a very puzzling phenomenon to the older helminthologists. 



(355.) The Proglottis, on becoming detached from the general com- 

 munity, is provided with all its organs ; nevertheless its development 

 becomes still further advanced : it even completely changes its shape ; 

 the angles of the segment become effaced, the whole body rounded, and 

 its movements, moreover, more extensive : nay, as Van Beneden assures 

 us, not only does the Proglottis continue to grow, but sometimes it 

 becomes as large as the entire Strobile a circumstance which fre- 

 quently causes a Cestoid at this age to be mistaken for a Trematode 

 Entozoon. 



(356.) Many thousands of eggs must be produced from such multi- 

 plied sources of reproduction ; and yet, how are they preserved and 

 replaced in circumstances favourable to their development? Fortu- 

 nately it is rare to meet with more than one of these creatures, at the 

 same time, taking up a residence in the same individual ; and, in fact, 

 the species which has specially been the subject of our description is 

 often called, par excellence, " the solitary worm," from this circum- 

 stance. Yet what becomes of the reproductive germs furnished in such 

 abundance ? Do they, as was the opinion of LinnaBus, live in a humbler 

 form in stagnant waters and marshes, until they are casually intro- 

 duced into the body of some animal, where, being supplied profusely 

 with food and placed in a higher temperature, they attain to an exu- 

 berant development ? Or are the germs thus numerous in proportion 

 to the little likelihood of even a few of them finding admission to a 

 proper nidus ? To these questions we can only reply by conjectures ; 

 and, interesting as the subject is, few are more entirely involved in 

 mystery. 



(357.) In some Ta3nise, as for example in T. serrata, which is found 

 in the intestines of dogs, M. Dujardin has pointed out that the ova, 



