NO. 3593 VICTORELLA — BANTA 5 



(suggesting an acid muco-poly saccharide). They are most abun- 

 dantly developed on the marginal portion of the frontal surface or in 

 the vicinity of the apertural papilla (fig. 1), but they may occur on the 

 connecting tubides as well. In some cases, filiform processes are 

 produced on the wall of the vestibide near the aperture so that, when 

 the lophophore is withdrawn into the zoecium, the detritus accumu- 

 lated on the neck of the extruded polypide is drawn directly into the 

 vestibule. Vestibular filiform processes can be seen protruding from 

 the apertures of the zoecia shown in figure 1. 



Digestive system. — The digestive system of form A is illustrated 

 in figures 3, 5, G, and 7. The lophophore, when retracted, is oriented 

 parallel to the surface and at right angles to the vestibule, which is 

 situated directly below the aperture (fig. 7). There are 11, 12, or 13 

 tentacles, 12 being the more common. 



Tlie short, ciliated pharyx passes into a spacious esophagus with 

 veiy characteristic elongate, vacuolated cells. The esophageal cells 

 pass insensibly into rounded eosinophOic cells of the cardiac stomach. 

 Here the digestive tract is interrupted by a single discrete band of 

 smooth muscle, the cardiac sphincter (fig. 3). The sphincter, without 

 visible nuclei, is immediately followed by a short, ill-defined reinforced 

 region. The caecum is broadly oval and distinctly flattened in the 

 frontal plane (fig. 6 and 7). The rounded intestine leads distad and 

 opens at the base of the setigerous collar. 



Muscular system. — The vestibidar musculature is strongly bi- 

 lateral in form A, originating distolaterally below the vestibule (fig. 6) 

 and inserting on the diaphragm. The arrangement is indistinguish- 

 able from that described for Arachnidium jihrosum by Marcus (1938, 

 p. 51) and Prenant and Bobin (1956, pp. 227-228). 



Reproductive system. — Testes in various stages of development 

 have been repeatedly observed in specimens of form A collected in 

 March 1965, but ovaries are uncommon. I have not seen an inter- 

 tentacular organ in a zooid of form A, but one is present in many form 

 B zooids. 



The apertural papilla. — The term apertiu-al papilla follows the 

 usage of Silen (1944, p. 26) and is equivalent to the "peristome" of 

 Ryland (1958, p. 317), the "tubular peristome" of Prenant and Bobin 

 (1956, p. 233), and the "upright cylindrical structure" of O'Donoghue 

 (1924, p. 59). In the typical form A zoecium, the apertural papilla 

 is low, rounded, and occupies only about a third of the length of the 

 zoecium (fig. 1). Transition from the A to the B form occurs through 

 the exaggeration of the apertural papilla and the assumption of vertical 

 budding of new zooids from the upright portion of the zoecial wall. 

 Although they may be distinguished readily in their extreme forms, 



