335] NORTH AMERICAX ASPIDOCASTRIDAE—STUXKARD 55 



the bulb contains a few granules or "concretionary bodies", but in struc- 

 ture these appear identical with the cutieular lining of the cavit.y. As 

 mentioned above the organs are located in the angles between the muscu- 

 lar ridges and the wall of the disc, and are set in a mass of non-staining 

 tibrous connective tissue. Some of the fibers pass dorsad from the bulb 

 between the muscular ridges to the limiting membrane of the disc, but 

 in appearance these are similar to the others and there is nothing to in- 

 dicate that they are nervous in character. However in one section, 

 stained with Heidenhain's iron haematoxylin, there is a nerve fibril pass- 

 ing around tlie bulb and terminating on the inner end of the heavy walled 

 portion of the canal (Fig. 55). Other nervous structures were not ob- 

 served. The connective tissue contains many nuclei, similar in size and 

 shape, and in no ease was a connection bet\veen these nuclei and the 

 marginal organ observed. No glandular cells and no evidence of a se- 

 cretion were found. In the studj^ of living specimens it was noted that 

 tlie marginal organs were everted and retracted as the worm moved. 

 Everted they appeared as membranous sacs and their movement was 

 rapid and precise. No evidence was found to indicate that these organs 

 l)0ssess a glandular function ; the character of their movement and the 

 nerve fibril leading to tlie canal as demonstrated incline the writer to re- 

 gard these structures as sensory. 



Similar organs have been reported as present in all the genera of 

 the family except Stiehocotyle. They were first noted in Aspidogaster 

 by Dujardin (1845) who described them as pores or orbicTilar glands. 

 Voeltzkow (1888) observed in Aspidogaster that they were protrusible 

 and retractile, and for this reason decided they w'ere sensory. Monti- 

 celli (1892) described them in Cotylogastcr michadis and supported the 

 idea of their sensory character. Niekerson (1902) described in Cotylo- 

 gastcr occid-entalis a bundle of fibers which he regarded as a nerve en- 

 tering the bulb at its basal end, and a cluster of bipolar nei've cells lying 

 upon tlie side of tlie bulb against which the canal is coiled when retracted, 

 lie stated that the presence of the bipolar cells establishes the sensory 

 character of tliese organs. He described the bulb as filled with vesicular 

 or granular material, and tho no nuclei were discernible, regarded 

 tliis as cytoplasm of granular cells in different stages of activity. 



Looss (1902) in Lophotaspis valid described two types of structures 

 as occurring in the interstices between the muscular ridges of the ventral 

 disc. Those around the peripherj' of the disc at the ends of the cross 

 ridges he called "marginal bodies" and those at the intersections of the 

 ridges he called "tentacles." The first he compared with the marginal 

 organs of other aspidogastrid genera, and the tentacles differ only slightly 

 in details of structure. He stated there was nothing in the structure 



