264 H. J. VAN CLEAVE 



ponent nuclei, for numerical constancy remained undisturbed. 

 In this case one nucleus normally in the anterior dorsal group had 

 taken a position on the ventral side of the body. Before trying 

 to explain this departure from the normal, attention must be 

 called to the following points : 



1. The nuclei in the dorsal line lie within the dorsal longitudi- 

 nal canal, and the one nucleus on the ventral side of the body 

 is similarly situated in the ventral canal. These two canals 

 communicate directly through the circular canals of the lacunar 

 system. 



2. Hamann ('91, p. 21) ascribes to the nuclei of an Echino- 

 rhynchus in the embryonic state the power of amoeboid move- 

 ment. 



3. Since it is a well-known fact that some nuclei may wander 

 to that part of the cell where they can best perform their functions, 

 and may even penetrate heavy cell walls in order to reach a 

 distant point of injury; may not the displacement of the nucleus 

 in the abnormal specimen of Eorhynchus gracilisentis just cited be 

 explained as the result of either active amoeboid movements which 

 carried it along the lacunae to the opposite side of the body, or 

 as a migration of the nucleus brought about by some local irritation 

 or injury of the body on the ventral side? 



In no other instance has the writer seen the parallel of Liihe's 

 figure of Eo. rutili (copied as fig. 31) in which he portrays four 

 dorsal and two ventral subcuticular nuclei (Liihe '11, p. 12, fig. 1). 



Eorhynchus longirostris. The nuclei of the subcuticula of this 

 species differ but little from those of the preceding species. In 

 the first place the median dorsal row of five nuclei is not so clearly 

 divided into an anterior group of two and a posterior group of 

 three nuclei. The nuclei of this region are almost equidistant one 

 from another. Moreover the terminal member of this series ap- 

 proaches nearer to the posterior tip of the body than does the ter- 

 minal nucleus in Eo. gracilisentis. The swellings upon the sur- 

 face of the body caused by the presence of these nuclei are more 

 distinct in toto mounts of Eo. longirostis than in mounts of the 

 preceding species. The dorsal nuclei have as an average, a long 



