CESTODARIA 439 



i.e. for about 16mm. Thus the ratios of the lengths of the 

 four regions to the length of the body in these two large and 

 small specimens respectively differed considerably, being ^^^^ 

 and 1^6 for the head, g^ and f^ for the testicular region, 

 ~l and j'i for the uterine region, and |^ and j-i for the post- 

 ovarian region ; but it is noteworthy that the combined lengths 

 of the testicular and uterine regions in each of the two specimens 

 occupied in each case about the same fraction of the body 

 length, i. e. ^^ and y|, both of which are roughly equivalent 

 to |. The head and the tail thus appear to be the variable 

 regions, as might be expected (vide infra). 



The head region is very variable in form. PI. 24, fig. 2, 

 represents what may be regarded as its normal semi-contracted 

 shape, but it can be elongated so that its outline becomes 

 indistinguishable from that of the succeeding testicular region 

 (PI. 24, tig. 3, a, b), or, on the other hand, contracted to form 

 a short globular mass (PI. 24, figs. 3, d, e, 4). When semi- 

 contracted there is often a short space between the broad base 

 of the ' head ' and the most anterior testes (PI. 24, fig. 2), Init 

 in many cases this space is absent. The surface of the head is 

 marked by deep longitudinal creases lined by thick cuticle 

 (PL 24, figs. 2, 3, 5, 6). These longitudinal creases vary in 

 number in different specimens — from 13 or 14 up to 25 or 

 26 — and are perhaps inconstant in the same individual, being 

 dependent upon the contraction of transverse musculature. 

 A transverse section through the base of the head (PI. 24, fig. 6) 

 shows well-marked longitudinal muscle-fibres scattered through- 

 out the parenchyma betw^een the thick subcuticula and the 

 central muscle-free medullary area, and conspicuous transverse 

 fibres running from side to side : muscle-fibres running obliquely 

 and dorso-ventrally are not conspicuous. The excretory 

 system lies at the base of the subcuticula and not on the edge 

 of the medullary area. A longitudinal section through the 

 contracted head (PI. 24, fig. 4) shows that the transverse band 

 often visible round and marking the base of the head (as shown 

 in PI. 24, figs. 2, 3, a) is due to a clustering of nuclei probably 

 belonging to muscle-fibres. The two main longitudinal nerves 



G S 2 



