THE ANATOMY OP PENTASTOMUM TERETIUSCULUM. 25 



but inasmuch as the structure which lies on each side of the 

 body has a definite relationship to the hooks, and, more 

 important still, there is a glandular mass which does lie in the 

 head region, it is advisable to retain the name of hook-gland 

 for the organ now to be described, more especially since in 

 doing this we are retaining the nomenclature of older workers. 

 At the same time it may be pointed out, as will be described 

 soon, that the hook- and head-glands are directly continuous 

 with one another, and the application of two distinct names is 

 merely a matter of convenience. 



In P. teretiusculum the large secretory gland of the body 

 may be regarded as consisting of an anterior unpaired portion 

 lying in the head region, from which on either side there 

 extends backwards a long branch which lies close beside the 

 alimentary canal, and reaches almost to the posterior end of 

 the body. The unpaired part forms the head-gland, the paired 

 part the hook-glands. 



The hook-gland of each side may be described as a long, 

 slightlytaperingjfinger-likemassof almost the same length as the 

 mid-gut, but not quite reaching either the anterior or posterior 

 extremity of this (figs. 6 and 7). The younger the specimen the 

 more compact is the gland, and in such forms there is often, 

 as described by Hoyle, the appearance of a fine membrane 

 enclosing the mass. In mature specimens such a structure is 

 rarely visible, but on opening the body-cavity the gland on 

 either side may be separated from the other organs as a dis- 

 tinct structure, save at the anterior end. In the mature form, 

 again, they are compressed and pushed out of place by the 

 swollen-out reproductive organs. 



In young forms there may be easily recognised a mesentery, 

 which at the anterior end of the gland serves to attach the 

 latter to the dorsal body-wall, another mesentery passing oflF 

 on the internal side to the wall of the alimentary canal (figs. 

 20 and 23, Mes^). The mesenteries, again, are more difficult 

 to recognise in the adult form, especially in the case of the 

 female. 



The gland has a definite relationship in position to certain 



