CESTODA. 661 



two ducts uniting, as is the case in many tape-worms inhabiting fish, e. g. 

 Tetrarhynchidae, Tetraphyllidae, Caryophyllaeus. Or, as in Bothriocephalus 

 and Ligula, etc. it consists of a large number of vesicles, lying close under 

 the subcuticula, and scattered over the sides of both aspects of the joints 

 in Bothriocephalus, over the dorsal aspect and the sides of the ventral 

 aspect in Schistocephalus and Ligula. The vesicles are connected by a 

 network of ductules from which a number of ducts proceed and unite into 

 a common vitello-duct 1 . The shell gland or ' Mehlis' gland' usually 

 consists of a large number of unicellular glands surrounding at one point 

 and opening into, the duct leading to the uterus. In T. lineata however it 

 consists of an inner layer of radial columnar cells and an outer of cells 

 more or less flattened. The uterus, apparently absent in Caryophyllaeus, is 

 a tube disposed in Taeniae with narrow joints, e. g. T. perfoliata, cross-wise, 

 but in other instances lengthwise, in the joints. It is convoluted and 

 opens externally by a separate aperture of its own in the Pseudophyllidea, 

 but in all other Cestoda it is closed, and as the ova accumulate, it 

 increases in size and may develope lateral offsets, especially in the larger 

 Taeniae, or it may become divided into several portions 2 . The vagina is 

 a narrow tube, of variable length, sometimes convoluted, often provided 

 with internal hooks or spines, and in most instances dilated at its inner 

 end to form a receptaculum seminis or spermatheca. In Schistocephalus 

 and Ligula, however, there appears to be no special dilatation, but sperm 

 collects at various points in the course of the tube. The innermost 

 extremity of the vagina generally ends in a tube which receives (i) the 

 ducts of the germaria, (3) the vitello-duct, and (3) the shell-gland, close to 

 the commencement of the uterus. Certain Taeniae, sometimes termed 

 generically Dipyliditim, e.g. T. elliptica of the dog, have in every joint 

 a right and left set of genital organs. But the uterus is common to the 

 two sets and has the form of a network with marginal caeca, and the 

 germarial ducts also enter the receptaculum seminis. The external aper- 

 tures of the cirrus and vagina are placed close together, usually in a 

 depression surrounded by a more or less prominent margin. The de- 

 pression or sinus genitalis has a single external pore. It is placed 

 commonly on one of the margins of the joints, frequently alternating 

 from one side to the other in successive joints. Or it is placed on the 

 ventral aspect of the joints as in some Taeniae*, and in the Pseudo- 



1 In Ligiila successive germaria are connected, according to Moniez. In both Schistocephalus 

 and Ligula the vitellarian follicles and testes do not appear, according to Kiessling, to be delimited 

 from one another in adjoining proglottides ; the vitellarian ductules are continuous throughout the 

 body ; A. N. 48, (i), 1882, p. 276. 



2 In T. lineata the ova accumulate finally in the cavity of the exhausted shell-gland which marks 

 the commencement of the uterus. A resistent calcareous shell is then formed round them. 



3 7\ lineata is an example. Hamann proposes the generic name Ptychophysa for these Taeniae. 

 Pt, lineata has (i) the aperture of the sinus on the surface of the joints; (2) the vagina opening 



