DEVELOPMENT OF SCOLICES. 39 



V 



worms, and so conveyed into the stomach. By the help of their 

 six hooklets they pierce its walls and pass into the perivisceral 

 cavity. Having got thus far, the immigrated tsenioid embryos 

 find in the meal-worms a fitting intermediate residence, and the 

 scoliciform agamozooid begins to be developed in them. The 

 embryos having thus completed their wanderings, and arrived at 

 their appointed end, throw off their boring apparatus, and play a 

 more subordinate part, the scoliciform agamozooid developed 

 within them, henceforward taking the chief place. The scolex is 

 itself sexless, but by asexual generation will bring forth sexual 

 individuals ; this, however, can only take place in the intestine of 

 some vertebrate animal, and it is now the turn of the scolices to 

 wander, in order that they may pass from their intermediate host 

 into their final one. 



In doing this the nurse is entirely passive, waiting until 

 its intermediate host shall be devoured by that particular verte- 

 brate animal which is fitted to serve as the nidus for its sexual 

 stage. What vertebrate animal this is, is at present unknown, 

 so that I can only speak conjecturally, and indicate that these meal- 

 worms are the favorite food of various small mammals, such as 

 rats and mice, and of numerous birds, the red-start, for instance ; 

 and that the Tenebrio molitor, which flies about, and is produced 

 from the chrysalis of the meal-worm, is often caught and eaten 

 by bats, swallows and other insectivorous animals. A minute 

 comparison of the scolices of the meal-worms with the heads 

 of tape-worms from the intestines of the animals I have named, 

 may perhaps assist in filling up the gaps in these observations. 



Another observation made long ago by myself, and which has 

 since been more fully worked out by Dr. Meissner, serves to 

 confirm the observations of Stein. In the substance of the pul- 

 monary sac of Arion empiricorum, (a slug), I discovered many 

 encysted scolices, 1 from the shape of whose heads I judged that 

 they formed part of the developmental series of a Ttenia. The form 

 of these scolices, is, however, very different from that of those 

 which are found in the meal-worms. Their head end is always 

 involuted in the short, and only partially developed, hinder 

 part of the body (fig. 20, 21). 



One sees in the whole arrangement of the various parts of the 



1 See my essay Ueber den Generationswechsel der Cestoden,' in the ' Zeitschrift ftir 

 Wissenschaftliche Zoologie/ 1850, p. 202. 



