CONTRIBUTIONS FROM THE ZOOLOGICAL LABORATORY OF THE MUSEUM OF COMPARATIVE ZOOLOGT AT 

 H.\RVARD COLLEGE. NO. 281. 



THE STRUCTURE OF METRIDIUM (ACTINOLOBA) 

 MARGINATUM MILNE-EDWARDS WITH SPECIAL 

 REFERENCE TO ITS NEURO-MUSCULAR MECH- 

 ANISM 



G. H. PARKER and E. G. TITUS 



SEVEN FIGURES (ONE PLATe) 



1. GENERAL STRUCTURE 



ERRATA 



The Journal of Experimental Zoology, volume 21, number 3, October, 

 1916. The chart on page 307 (E. R. Hoskins) is Chart 3 and belongs on page 

 311. The chart on page 311 is Chart 1 and belongs on page 307. The descrip- 

 tion of Chart 1 on page 307 refers to the chart on page 311, and the description 

 of Chart 3 on page 311 refers to the chart on page 307. This slip should 

 be pasted on page 307 when the volume is bound. 



tended, having a diameter decidedly greater than that ot tne 

 column. It is marked by a system of somewhat irregular rays 

 that indicate the lines of attachment for the mesenteries within. 

 It often produces a dense brownish secretion that covers the 

 surface to which the animal is attached and that is best seen 

 in individuals that have been continuously resident on one spot 

 for a long time. 



The column is an approximately cyhndrical portion which 

 narrows from the expanded pedal disc to a region of more uni- 



433 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 21, NO. 4 

 NOVEMBER, 1916 



