320 THE ANATOMY OF CESTODES. 



modifications by the more or less independent development of the 

 caecal tube. This is especially true of Bothriocephalus (sensu stricto) and 

 Ligula, in which these lateral tubes are broken up into a large number 

 of round or oval sacs (Fig. 170), which insinuate themselves between 

 the so-called " subcuticula " and the longitudinal muscles, and when 

 in their usual position, are found not only in the borders, but also over 

 a great part of the lateral portions of both surfaces. Their contents 

 consist mainly of the somewhat large and coarse-grained yolk-cells. 

 These pass into the fertilising canal by means of a branching system 

 (Eschricht's " yellow canals)," and finally in the shell-gland, or in the 

 commencement of the uterus, become enclosed in a firm shell, along 

 with a pale and membraneless ovarian egg. 



At first sight the differences between these yolk-glands of the 

 Bothriocephcdi and the above- described corresponding organ of the 

 Tseniadae appears so striking that one feels inclined to adopt the view 

 of Sommer, who calls the latter an " albuminous gland," and dis- 

 tinguishes it from the " yolk-gland " of the other Cestodes. And this 

 seems all the more likely since the nature of the secretions is different, 

 for while the products of the yolk-gland are granular cells, the albumi- 

 nous gland yields a tough and almost homogeneous fluid. Yet this fact 

 is of little significance, for many differences are also found in the 

 secretion yielded by the yolk -gland, which in the latter instance are 

 dependent on the degree and nature of the breaking up of the cells 

 yielded by the glandular wall In considering these conditions it 

 must not be forgotten that the structures in question do not produce 

 an ordinary yolk, but an envelope for the egg, which, however, like 

 the granular yolk, furnishes nutriment for the embryo, but in its 

 relation to the true egg more nearly resembles the albumen of the 

 bird's egg. For this reason it has often been proposed (especially by 

 Eeichert) to change the name " yolk-gland " for " albumen gland." 



Albumen gland and yolk-gland in these worms are, however, by 

 no means to be regarded as physiological contrasts, or at least they 

 are not so different as might perhaps have been supposed ; and it seems 

 to me also, that in the conditions existing in the Cestodes there is 

 hardly any difference morphologically between the organs in question. 



In support of this statement, I may refer to the structure of the 

 yolk-gland in Caryophyllceus, which, besides the two posteriorly 

 situated lateral tubes, also exhibits a middle portion, corresponding in 

 position and arrangement to the albumen-gland of the Taeniadse. If 

 we suppose the lateral organs to disappear and this supposition is 

 justified to some extent by the smaller yolk requirements of the 

 Tieniadae then the only difference left is that in Caryophyllceus the 

 remaining structure belongs to the cortical layer, but in the Taeniada 1 



