TAPEWORM. 227 



The nervous system of Bothriocephalus and Ligula is said to be simpler 

 than that of the Taeniae. 



The excretory system of T. serrata appears to correspond in its main features 

 with that of most Taeniae, a general description of which is given in the account 

 of the Class Cestoda. Ciliated funnels have been detected by Fraipont in this 

 Tapeworm and in its Cysticercus (Archives de Biol. i. 1880, p. 439). Leuckart 

 figures the anterior anastomosis between the longitudinal vessels as consisting of 

 a ring-like vessel with branches in connection with it (Parasiten (ed. 2), i. p. 379, 

 fig- Z 53)- Two longitudinal vessels are certainly present, perhaps four. P. J. 

 Van Beneden does not figure a cross anastomosis at the posterior margin of each 

 joint, nor does he mention the presence of valves ; points which lack of material 

 has prevented me from determining. He mentions, however, that treatment of 

 the scolex with acetic acid causes an evolution of Carbon dioxide in the excretory 

 canals which escapes by the foramen caudale or aperture of the pulsatile vesicle. 



Peculiar rounded or elliptical bodies of a bright refractile appearance are 

 found in the head and neck, and in the joints, especially the young joints, of 

 all Cestoda. These bodies are very numerous in T. serrata. They are found 

 principally in the superficial part of the connective tissue, but may occur also 

 in the more central part where they are absorbed on the evolution of the sexual 

 organs. They often show concentric lines like those of starch granules, and under 

 the action of an acid they give off a gas, Carbon dioxide, which exists in com- 

 bination with lime. Hence the name Calcareous bodies given to them. They 

 contain a small amount of organic matrix, and are believed to be either calcified 

 cells or portions of calcified cells. They lie, according to Griesbach, in the 

 lacunae of the connective tissue, and he appears to think that they may enter 

 the excretory system through direct communications between its cross anastomoses 

 and the coelomic lacunae. It is certain that the excretory canals contain calcareous 

 particles, and in certain Trematoda their branches have appended ampullae, in 

 which lie calcareous bodies similar to the calcareous bodies of the coelomic lacunae 

 in the Cestoda. The function of these structures is unknown ; it may be partly 

 excretory, partly skeletal. 



For the generative organs of a Taenia, see PL xiv. (post\ figs. 2 and 3. 



The structure and development of the ovum in T. serrata have been carefully 

 studied by E. Van Beneden. It consists of a delicate shell containing a germ 

 or ovum-cell together with a quantity of a hyaline, homogeneous and colourless 

 albumen or deutoplasm (= secondary yolk). The germ segments into two cells, 

 one transparent, the ' embryogenic globe,' the other a ' granular cell,' which 

 segments no further. The former of the two divides, and the result of its division 

 is a number of cells of which (i) three are larger and constitute the 'albumino- 

 genous layer ; ' (2) the remainder are smaller and constitute the ' embryonic mass.' 

 The three cells (i supra] enlarge and surround together with the 'granular cell,' 

 the ' embryonic mass,' and secrete a delicate superficial cuticle, the cell-limits 

 becoming indistinct. In the 'embryonic mass' there are three, four, or some- 

 times five flattened cells placed laterally and containing, unlike the remaining 

 cells, nucleolated nuclei. These cells constitute a ' chitinogenous layer.' They 

 give origin to (i) a superficial homogeneous coat; (2) a coat or shell of radially 

 placed juxtapposed chitinoid cylinders which increase in length at the expense of 



Q2 



