336 ORGANS OF DIGESTION'. 



of a small white prominent head or papilla terminated anteriorly 

 with a double row of minute, sharp, conical recurved spines 

 (A. .), and presenting around its sides four circular ab- 

 sorbent orifices (A. b.) From these orifices (A. b.} the ab- 

 sorbed fluids are conveyed by four slender canals through 

 a narrow neck (A. c.) into a thin transparent white mem- 

 branous sac (A. d. e.} more or less distended or contracted, 

 according to the state of repletion, and according to the pe- 

 culiar forms of the species. In the collapsed state of this 

 digestive bag, its anterior part (A. d.) assumes a narrow, 

 elongated, and corrugated form, and becomes more dense, 

 white, and opaque, with numerous transverse constrictions 

 which give it already an articulated appearance. A more 

 compound zoophytic form is seen in the ccenunts where nu- 

 merous minute heads, similarly constructed to those of the 

 cysticercus, open into the same common digestive sac or 

 vesicle. These heads are disposed in numerous groups over 

 the surface of a large transparent gastric cavity, and appear 

 as clusters of opaque white points. A small detached por- 

 tion of the general digestive sac of the ccenurus cerebralis, 

 highly magnified, and with three of the absorbent heads 

 preserved in different states of extension, is seen in Fig. 1 16 B. 

 The anterior terminal papilla of each head is surrounded, 

 as in the cysticercus, with a double row of recurved spines 

 (B. a. .), and around the dilated part of the head are the 

 usual four perforated suctorial disks (B. b. b.) The head is 

 attached to a narrow neck (B. c. c.) 9 capable of consider- 

 able elongation and contraction, and these passages all lead 

 to the same capacious general digestive vesicle (B. d.) 

 In the long flat cestoid forms of parenchymatous entozoa, 

 the structure of the head, with its absorbent pores, is very 

 similar to that of the hydatids. Around the anterior 

 median papilla of the tcenia, which is sometimes perforated 

 with a small pore, there is a double range of minute re- 

 curved sharp spines, and the four lateral perforated suckers, 

 disposed on the four angles of the head, lead to as many 

 canals, as in the cysticercus. The upper and lower canal 

 however on each side unite with each other to form one, and 

 these two lateral canals, thus constituted of the original 

 four, extend along the two sides of all the segments of the 

 body, as seen in two of the segments magnified of the tania 



