40 THE TAPE-WOEM. 



encysted scolex with the retracted head, that the latter is pro- 

 duced in exactly the same manner as that of the meal-worm 



scolex described by Stein, viz., by in- 

 ternal pudding, although I have never 

 chanced to meet with such earlier stages 

 of development of the scolex in the slug. 

 However, that they do directly emanate 

 from Tcenia embryos, is evidenced by the 

 three pair of hooks or claws, which are 

 firmly fixed in the substance of the sur- 

 face of the posterior extremity of the 

 body of these retracted scolices. We are 

 indebted to Dr. Meissner for the discovery that these six claws are 

 the remains of the embryonic condition of these cestoid agamozooids. 1 

 The encysted scolices in the slug, therefore, are perfectly analo- 

 gous in form and signification to the cestoid agamozooids in the 

 meal-worm, with this difference, that the first are not elongated 

 into a tail at the posterior extremity. The encysted cestoid 

 agamozooids in the slug are evidently the result of the immigra- 

 tion of cestoid embryos, and yet in spite of the fact that 

 these parasites are very frequently met with in slugs, 2 I have 

 not been able to determine which species of Taenia- embryo passes 

 into this form of scolex, nor into the intestine of what particular 

 vertebrate animal the scolex of the slug must emigrate, to give 

 rise to sexual individuals. 



The sexually matured individuals of the Cestoidea are no other 

 than their full-grown joints; in which are developed the male 

 and female genitalia, by whose co-operation eggs capable of re- 

 production are generated, and the continuation of the species is 

 secured. Such a sexually-mature, hermaphrodite joint of a 

 cestoid worm, which, in certain genera of Cestoidea, when fully 

 formed, separates from the body of the scolex with great 

 readiness, is denominated a Proglottis. The formation of these 



Fig. 20. A scolex of Tania from Arion empiricorum included within its receptacle. 

 Fig. 21. The same extruded, a. Head of the scolex. b. Receptaculum scolicis. c. The 

 remains of the six embryonic booklets. 



1 See the ' Zeitschrift fur Wiss. Zool.,' B. v, 1854, p. 383. 



2 I have found, not only in Breisgau, but also in Schleswig, and here in Bavaria, the 

 lung of the red slug (Arion empiricorum) very frequently infested by the encysted 

 scolices referred to above; and I learn from Dr. Meissner that the same is the case with 

 the slugs found in the neighbourhood of Hanover. 



