44 W. A. HERDMAN. 



The rhinophores are large, and are placed in the usual position 

 on the head. Each of them has its upper half strongly 

 laminated or marked with parallel transverse ridges, while 

 near the base of each two simple tapering branches arise, the 

 one directed horizontally forwards and the other rather out- 

 wards to the side. There are three branchial plumes, which 

 are placed in the centre of the dorsal surface. The largest one 

 is median and anterior, and the other two form a pair placed a 

 little further back : they are all much branched. 



The cerata form a series of five erect, rod-like processes 

 along each side of the back. They extend from the centre 

 nearly halfway to each end of the body, and thus form a 

 protecting palisade along the middle third of the back, at 

 each side of the branchiae. 



In sections through the front of the head (fig. 4) it is seen 

 that the branches of therhiuophore are, like the cerata further 

 back, prolongations upwards of the body-wall composed of 

 ordinary mesodermal tissue containing only the usual small 

 blood-lacunae. A few sections behind (fig. 5) we come upon 

 the rhinophore proper, showing the broad lateral laminae, 

 while the stem contains a large bundle of nerve-fibres and, 

 further up, a ganglionic mass of nerve-cells (fig. 5, g). 



Some way further back in the body the cerata and branchiae 

 are seen in section. Fig. 6 shows in the centre the basal 

 part of the first or median branchia cut near its anterior end. 

 It contains a large blood-cavity. On each side is seen one of 

 the cerata, that on the right having had several undulations near 

 its middle. These cerata are seen from this and neighbouring 

 sections to be direct continuations upwards of the ectoderm 

 and mesoderm of the body-wall, and to contain no special struc- 

 tures beyond the epithelium and the connective and muscular 

 tissues of the integument (fig. 6) . There are many small blood- 

 lacuuEe in the mesoderm, but these are not more numerous nor 

 larger than the corresponding spaces in the body-wall, and 

 nothing approaching the structure of a branchia is seen. 



PI. VII, fig. 7, shows a section further back where the 

 median branchia is cut through longitudinally about its central 



