STRUCTURE OF CLINOSTOMUM 197 



30) found organs of much the same kind in the oral sucker of 

 certain distomes. Pratt ('09, fig. 10) copies a figure of a section 

 of the body wall of Ligula, one of the cestoda, from Zerneke. The 

 section made by the Golgi method shows nerve cells located some 

 distance below the cuticle from which threads run outward to 

 small spherical ' sense organs' located in the basal level of the cuti- 

 cle. These organs and those of Nickerson are similar in struc- 

 ture to those of Clinostomum. In Cotylaspis (Osborn, '-04, fig. 

 33) the cuticle contains organs apparently of sensation but of a 

 different type from these. They are in the surface of the cuticle 

 and communicate with the exterior. They have a number of 

 stainable fibers which unite and pass as a single thread inward 

 through the cuticle and disappear in the parenchyma. Nicker- 

 son, in the article just referred to, in his fig. 14 has shown an organ 

 in the cuticle which communicates with the exterior. 



Muscles of body ivall. The usual muscles are present as in 

 trematodes at large. Figs. 6 and 7 show them in longitudinal 

 and transverse section respectively. In addition to them there is 

 a layer of longitudinal muscle, which lies immediately below the 

 cuticle. This is an unusual layer of longitudinal muscle, the usual 

 one being located inside the circular muscle, while this is exter- 

 nal to it. * We may designate it the outer longitudinal muscle 

 (mo) the other being then called inner (mi) in the figures. The 

 fibers of this outer longitudinal layer were seen by Looss ('85) and 

 are shown in his fig. 23. According to his figure they are very 

 much stronger than I find them in my sections. In my material 

 the fibers are exceedingly small, having a diameter of only 0.0009 

 mm. In fig. 7 they are shown under a magnification of 1100 

 diameters. Their size can perhaps be better appreciated by a 

 comparison with those of the inner longitudinal layer as seen in 

 figs. 6 and 7. In the latter the fibers are cut transversely. These 

 fibers lie at equal distances apart, in a single layer, and in direct 

 contact with the cuticle. 



Writers who have given attention to the finer structure of 

 trematodes (Braun, '93; Otto, '96; Stafi"ord, '96, to mention three 

 at random) agree that there are three layers which compose the 

 musculature of the bod,v wall, viz: circular, longitudinal and 



