254 



MR. H. A. BaYLIS and LT.-COL. CLAYTON LANE ON 



GNATHOSTOMIN^ *, subfam. n. 



The members of this subfamily are characterized by the 

 possession, immediately behind the lips, of a cuticular swelling, 

 which we term the " head-bulb."' This head-bulb always con- 

 tains four subglobular, submedian, inembranous structures, for 

 which we use the expression ballonets." Each of these is 

 connected by a narrow neck with one of the four organs which 

 have been called by several anchors "cervical glands," but which 

 we prefer to name " cervical sacs." The latter are elongated, 

 apparently unicellular, thick-walled, hollow, blind organs hang- 

 ing freely into the body-cavity at the sides of the oesophagus. 

 Externally tliey are provided with a coat of fibrils show^ing a 

 spiral arrangement (text-fig. 17) and probably contractile. The 

 protoplasm lining the sac internally probably secretes a fluid into 

 the lumen. 



The cuticle of the head-bulb may be simply raised into 

 transverse ridges or pronounced striations with projecting 

 posterior edges ; or the striations may be beset with rows of 

 chitinoid hooks, strongly resembling the " rose-thoiii " type of 

 hooks found in certain Ces^todes, such as Bipylidium. The 

 hooks are embedded by means of their own roots in the cuticle, 

 and are not merely outgrowths of the cuticle itself. 



The external surface of the head-bulb may be unaffected by 

 the presence of the ballonets within ; or may be indented 

 between the ballonets so as to give an external expression of 

 the internal structure. Between the ballonets, sometimes push- 

 ing in the ballonet-membranes before them, certain muscles run 

 up to the lips, crossing the cavity of the head-bulb obliquely in 

 such a way that when contracted they serve to shorten the 

 head-bulb in an antero-posterior direction. The function of the 

 head-bulb is probably to act as a burrowing-organ or holdfast. 

 The worms presumably first bury their heads in the tissues of 

 the host while the head-bulb is in a deflated condition, and then 

 the cervical sacs, contracting, force their contained fluid into the 

 ballonets, thus distending the head-bulb. The cuticular stria- 

 tions and hooks are additional structures rendering the whole 

 apparatus more effective. 



These various structuies, with the exception of the ballonets, 

 have been noted by previous writers, but quite a different inter- 

 pretation has usually been put upon them. Fedchenko (1872), 

 working on GnatJtostoma hisjjidtLm, seems, according to our 

 translator, to have believed that the matter inside the head was 

 secreted by the four cervical sacs, and he thus comes nearly to 

 our own conclusion. Hfe notes the structureless necks into 

 which the sacs pass, but has observed no actual connection 

 between the sacs and the head-bulb. On the other hand, the 

 prevailing interpretation is due to v. Linstow, who describes 



* For sul)famil3' diagnosis, see p. 255. 



