2ao NATURAL HISTORY BULLETIN. 



been found with two, three, or four pairs, and when only two 

 pairs were present they were not opposite each other, but 

 were separated on one side by one pair of the first cycle and 

 on the other side by three pairs. These irregularities seem 

 to be characteristic of the species, since out of seven speci- 

 mens examined not one showed what is usually regarded as a 

 typical arrangement. The condition described by G. Y. and 

 A. F. Dixon ('89) for B anodes thallia is thus recalled. 



The longitudinal muscles of the perfect mesenteries were 

 well developed, the long mesogloeal processes radiating out in 

 a somewhat fan-like manner from a thickened portion of the 

 mesentery (PI. 11, Fig. 3). The parieto-basilar muscle was 

 also well developed on these mesenteries, but on those of the 

 second and third cycles, which lack mesenterial filaments, the 

 musculature was borne by a number of short processes ar- 

 ranged equally on both sides of the mesenteries, those on one 

 side representing the longitudinal muscle processes and those 

 on the other the parieto-basilar processes. Acontia were 

 present but were few in number. I found reproductive organs 

 in only two of the specimens examined and in these they 

 occurred on the mesenteries of the first cycle, the directives 

 included. In both cases, however, they were immature, 

 though it seems probable that even when mature they are 

 limited to the mesenteries of the first cycle, since those of the 

 second and third cycles lack that portion of the mesentery 

 which corresponds to the reproductive region of the first cycle 

 mesenteries and possess only the muscular region. 



A well developed sphincter of the mesogloeal type occurred 

 in the upper part of the column wall. It was of an elongated 

 oval form in section (PI. 11, Fig. 4) and the area which it 

 occupied was traversed by numerous strands of mesogloea, 

 running in the direction of the thickness of the column wall 

 and anastomosing somewhat so that the spaces occupied by 

 the muscle fibres were somewhat spindle-shaped. The area 

 occupied by the muscle was sharply marked off as a rule, 

 though occasionally a few detached and scattered muscle 

 cavities were observed. 



