CELL CONSTANCY IN THE GENUS EORHYNCHUS 263 



arrangement, that variation beyond that which is capable of 

 explanation on the basis of the degree of contraction is limited 

 to a single instance. Each one of more than two hundred indi- 

 viduals had six nuclei in the subcuticula, arranged according to 

 the following system: Five large nuclei occupy positions in the 

 mid-dorsal line of the body. Three of these constitute a group 

 toward the posterior end of the body while the remaining two are 

 separated slightly farther from the rest and lie anterior to the 

 group of three, but are included in the same sagittal plane as the 

 posterior nuclei. In sexually mature individuals these nuclei aver- 

 aged 0.078 mm. by 0.045 mm. The sixth nucleus of the subcuti- 

 cula is located in the mid-ventral line, near the anterior end 

 of the body, usually at a point between the anterior and pos- 

 terior groups of the dorsal series. It is more elongated and larger 

 than the other nuclei of this tissue, having a long axis of 0.125 

 mm. and a smaller diameter of 0.050 mm. These nuclei are ir- 

 regularly ovoid in shape, though occasionally they are reniform as 

 shown in figure 4, sn.5. The chromatin usually has a closely 

 compacted arrangement, but sometimes takes the form of an 

 irregularly branching network within the nucleus. The shape 

 of the nuclei in this tissue of the Eorhynchi is in decided contrast 

 to that described by Graybill ('02) for the nuclei of the subcuti- 

 cula of Echinorhynchus thecatus Linton. According to that 

 writer the nuclei of this last named species are of a wonderfully 

 dendritic nature, each having a broad expanse of finely branching 

 processes. The contrast is none the less striking if a compari- 

 son be made with the subcuticular nuclei of any other type of 

 Acanthocephala. Three types of subcuticular nuclei are thus dis- 

 tinguishable in the Acanthocephala; the giant nuclei of the Eo- 

 rhynchi, the dendritic nuclei of E. thecatus, and the numferous 

 small nuclei scattered throughout the subcuticula as in most 

 other Echinorhynchi and some of the other genera. 



Only one specimen of all the Eorhynchi examined showed 

 variation in the number and arrangement of these nuclei such 

 as might be expected, judging from the statement of previous 

 investigators. This individual was a small, immature female. 

 Even here the variation was purely one of arrangement of the com- 



