THE CESTOIDEA 107 



the necks of gland cells or a nerve fibre. There can be no doubt 

 that the " subcuticula," of which there have been various interpreta- 

 tions, as in the case of Trematodes, is a true epidermis, consisting 

 of spindle-shaped cells which send fine processes upwards through 

 the basement membrane, to cease at the cuticle. The epidermic 

 cells form a continuous "epithelium" in Triaenophorus, but this 

 continuous sheet is interrupted in Ligula, and still more in Taenia 

 and the majority of Cestoidea, by intrusive parenchyma, which may 

 also be accompanied by muscle fibres ; indeed, in Taenia the thin 

 layer of circular, and the longitudinal coat of the " dermal " muscu- 

 lature come to lie between the "subcuticula" and the basement 

 membrane. 



The bulk of the musculature, however, lies below the " sub- 

 cuticula " ; the outer coat of the parenchymal musculature consists 

 of longitudinal fibres, which in the young part of the chain (or 

 throughout the worm in Ligula) are continuous from one proglottid 

 to another ; but as these become more and more deeply constricted, 

 the muscular coat becomes interrupted ; in the higher Cestodes this 

 longitudinal coat is often separated by parenchyma into outer and 

 inner layers. The inner muscular coat consists of a sheet of 

 transverse fibres on the dorsal and on the ventral surfaces, dis- 

 continuous at the right and left margins ; these transverse muscles 

 are also, at first, continuous from joint to joint ; they delimit a 

 central or medullary part of the parenchyma from a cortical part. 

 In the Cestoidea, as in the Trematoda, the same controversy has 

 raged as to the character of the parenchymal tissue ; the most recent 

 investigations, and the use of the most modern methods, tend to 

 show that the parenchyma consists of very greatly branched cells, 

 the processes from which, nutritive in function, extend in all 

 directions, and are extensively ramified (Blochmann). These cells 

 lie in a homogeneous matrix, containing vacuoles filled with a 

 coagulable fluid. This ground substance, which is not cellular, as 

 Leuckart and others believed, extends right up to the basement 

 membrane, interrupting the continuity of the epidermic layer of 

 cells. In this parenchyma, and chiefly in its cortical region, are the 

 characteristic " calcareous corpuscles." Each is structurally very 

 similar to a fat cell that is, the concentrically marked spherical 

 concretion of lime is enveloped in a protoplasmic membrane, the 

 nucleus being on one side (Blochmann). These lime corpuscles con- 

 sist of about 21 per cent of lime, the rest being organic substance; 

 the lime is in the form of carbonate, partly of albuminate (Griesbach), 

 and perhaps even of a certain amount of urate. Originally 

 considered as an excretory product and described as lying in the 

 excretory canals, which they do not they are now usually regarded 

 as "skeletal" (Leuckart), or as counteracting the acidity of the 

 gastric juices. However, they do not disappear with age ; nor is it 



