J. Johnstone 
395 
more immature proglottides they form a very uniform layer, but in the 
more mature segments they are arranged in irregular bundles as is 
shown in Fig. 21, the bundles being elongated at right angles to the 
integument. 
In the region of the scolex a second series of transversely running 
fibres may be present just internal to the longitudinal layer; these are 
shown in PI. XXIII, fig. 19. They are quite absent in the mature pro¬ 
glottides. In the scolex other muscle fibres may also be present; some 
of these run dorso-ventrally, or a.t right angles to the axis of the scolex 
in various planes; and some are evidently the prolongations of myo¬ 
blast. But the true integumentary muscles consist of smooth unstriated 
fibres without cell bodies or nuclei. They always stain a bright red 
with methyl-blue-eosin. 
The integument as above described varies only to a slight extent 
in different parts of the body, the chief modifications being those of the 
arrangement of the muscle layers. 
VI. The immature ‘proglottis. 
The male genital organs. The following account of the anatomy of 
the proglottis, which I hope will add materially to our knowledge of the 
morphology of the Tetrarhyuchids, is based almost entirely on the study 
of serial sections. Stained and cleared preparations of the whole 
proglottis help us very little in this respect, for the segment is nearly 
cylindrical in shape and can be flattened out to a very slight extent. 
The larger genital organs can indeed be made out but it is quite 
impossible to attempt to trace the relations of the ducts. The recon¬ 
struction of the organs from a complete series of sections is therefore 
the only practicable means of studying the anatomy of the proglottis. 
PI. XXI, fig. 10 is a reconstruction of the genital organs present in 
the immature proglottis and has been reconstructed from a complete 
series of transverse sections ; it should be compared with Text-fig. 8, 
which represents a transverse section through a proglottis in the same 
phase. The former figure is slightly diagrammatic, that is the coils of 
the vas deferens and uterus are made less complex than they ought to 
be and the vitellaria are drawn as if they were two bands along the 
lateral margins of the segment: in reality they are present all round 
the periphery of the latter. The ovary is situated at the posterior end 
of the proglottis and the genital aperture is at the postero-lateral 
margin. From this common genital aperture two ducts proceed : one, 
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