CESTODA. 665 



on p. 225. The Cat gives shelter to T. crassicollis (supra] and T. elliptica 



(P- 325). 



The duration of a Cestode's life is unknown. It probably varies. The pro- 

 scolices of Echinococcus ( = hydatids, acephalocysts) have been known to persist for 

 thirty years, and the strobila of T. mediocanellata five, six, seven, nine, or even 

 eleven years. A Cysticercus cellulosae (=7*. SoKum) has been observed in the eye 

 for twenty years. 



Archigetes Sieboldi, which occurs in a sexual scolex stage in the coelome of 

 Tubifex rivulorum, an Oligochaete, is about 3 mm. long. It consists of an oval 

 body, the scolex, about 1-1-3 mm - l n gj an d a cylindrical tail, the proscolex, which 

 is attached to a pit at the end of the body, and bears at its other end three pairs of 

 hooks. Both parts are capable of motion. The scolex has two grooves, one on 

 either side the head. There are eight longitudinal excretory vessels, and a vesicle 

 opening at the insertion of the tail. The testes are placed anteriorly ; the vitellaria, 

 one on each side of the body. The genital aperture is ventral, and is the common 

 exit of the vas deferens, a vagina or oviduct, and a uterus separate from the latter. 

 Leuckart, Z. W. Z. xxx. 1878, Suppl. ; Gruber, Z. A. iv. 1881. 



The family Amphilinidae contains two genera, Amphilina from the coelome of 

 the Sturgeon, Amphiptyches from the intestine of Chimaera. The body is flat, and 

 like that of a Distome, with a sucker at its anterior pole. In Amphilina a number 

 of unicellular glands open into the sucker 1 , and are surrounded by the retractor 

 muscles of that structure. Its nervous system consists of two anterior swellings 

 connected by a transverse commissure, and two lateral nerves, which unite pos- 

 teriorly and give off branches. The testes are vesicular; the vas deferens opens 

 posteriorly ; the germarium is single, the vitellaria double, one on each side, and 

 structurally resembling the same organs in a Trematode ; the vagina opens near the 

 vas deferens, the uterus anteriorly. The embryo is ciliated anteriorly, and has ten 

 hooks. The family has been supposed to connect the Cestoda and Trematoda. 

 Cf. Lang, Mitth. Zool. Stat. Naples, ii. 1881, p. 394; Salensky, Z. W. Z. xxiv. 1874; 

 Grimm, Z. W. Z. xxv. 1875. Amphiptyches, Wagener, Archiv f. Anat. und Physiol. 

 1852; cf. Id. A. N. 24, i, 1858. 



The Class is divisible into the following groups, the value of which is uncertain, 

 but they are generally regarded as families. 



1. Taeniadae : head provided with four suckers, and sometimes with a single 

 or double circlet of hooks. Proglottides well-defined and cast off. No uterine 

 aperture. Taema, Ptychophysa ?, Dipylidium ? 



2. Tetraphyllidae : head with four very mobile and distinct suckers. Pro- 

 glottides well-defined and cast off; inhabit Selachians. Subdivisible into (a) Phyllo- 

 bothridae, e. g. Echineibothrium, Phyllobothrium ; and (b) Phyllacanthinae^ with 

 two to four hooks to each sucker, e. g. Calliobothrium. 



3. Tetrarhynchidae ( = Phyllorhynchidae) : head provided with four suckers and 

 four protractile proboscides armed with hooks. Non-sexual form occurs chiefly 

 in Teleostean fishes, the sexual in ElasmobranchiL Tetrarhynchus. 



4. Diphyllidea : the neck and two suckers armed with hooks. Echinobothrium, 

 in the Ray. 



1 Traces of this sucker are found together with glands in some Tetrarhynchidae. See Lang, 

 cited below. 



