56 ILLINOIS BIOLOGICAL MONOGRAPHS [336 



of the marginal bodies to warrant the former belief in their sensory 

 character. Granules in the cavity he regarded as droplets of a secretion ; 

 and in the connective tissue dorsal to the cavity he described sac-like 

 spaces with fine granular contents, and he found also nuclei but was un- 

 certain whether they lay in the spaces or between them. The marginal 

 bodies he regarded as glandular organs altho doubtful as to their exact 

 function. He described the tentacles as having a spindle-shaped cavity 

 with glandular apparatus around the inner end, and a canal leading from 

 this blind end to the limiting membrane which formed the dorsal wall of 

 the musculature of the adhesive disc. He considered these structures as 

 adhesive or absorptive, but states that their physiological significance 

 was doubtful. 



Osborn (1904) in C. insignis described the marginal organs as con- 

 sisting of three parts, the canal with its muscular wall, the cavity, and a 

 dorsal fibrous part. The fibrous part he regarded " as a trunk of nerve 

 fibers running at least to the muscles of the organ and perhaps partly 

 sensory as well." The central cavity possessed "a lining of moderate 

 thickness composed of cuticle outwardly but of nucleated epithelium on 

 the inner side." This cavity he found empty or with one or more "con- 

 cretionary objects. ' ' He says, ' ' This indicates that secretion is going on 

 the products being removed from time to time. I think the muscles de- 

 scribed above may be used in discharging these products, the longitudinal 

 fibers may act as dilators of the outlet, needed to enable such large ob- 

 jects to make their escape. ' ' Later he states, " I do not find in Cotylaspis 

 any evidence of a glandular structure in the fibrous part, and do con- 

 sider the bulbous part as epithelial and secretory." 



The marginal organs apparently differ somewhat in structure in 

 the different genera. Of all the authors. Loess alone seems to have 

 morphological evidence for his conclusion that in Lophotaspis they are 

 glandular in character. The statement of Osborn that in Cotylaspis 

 insigtiis the bulb is partly lined with cuticula and partly with secretive 

 epithelium, I regard as doubtful. Certainly in my sections of that spe- 

 cies (Fig. 56) the bulb is lined with cuticula thruout. In the dorsal part 

 of the cavity shown there are many small structures but they appear to 

 be composed of the same material as the lining cavity. If they are cutic- 

 ular, this would argue against the glandular character of the organ since 

 in its functional activity the material wovild be swept out with the secre- 

 tion instead of accumulating and forming such large objects as he shows 

 in his figure. Furthermore it would be almost if not entirely impossible 

 for such large bodies to pass thru the small canal which leads to the ex- 

 terior. These "concretionary objects" are apparently the only basis 

 for Osborn 's claim that the organs are glandular since he stated that he 



