108 W. BLAXLAND EENHAM. 



which varies considerably in thickness, and can be traced, as 

 Boveri's figure shows, into the rod at each extremity (PI. 6, 

 fig. 12). This cutis stains exactly like the rod in cochineal, 

 and also like the rod is unstained in hsematoxylin. Sometimes 

 the cleft in the rod is more pronounced, and gives rise to a more 

 definite channel (see Lankester, xxxvi b, fig. 3, /) open to the 

 ccelom. Such a condition of things is represented in my PI. 

 7, fig. 31, which passes through a primary rod (P. 1) at the 

 level of a synapticulum,^ and should be compared with certain 

 variations in the rod of the tongue bar in the same figure and in 

 fig. 15, and one is struck with the resemblance between the two. 



I would suggest that the distinction between the two rods, 

 viz. that of the primary bar and that of the tongue bar, is not 

 so profound as one would be led to think from the use of the 

 terms solid (or bifid) rod and hollow rod. ^Ve have seen that 

 not infrequently the rod of the tongue bar is formed of two 

 pieces (fig. 15), whilst, on the other hand, the rod of the 

 primary bar may enclose a cavity. But I think the real dis- 

 tinction between them is that in the tongue rod the subepi- 

 thelial portion is usually and typically as thick as the sides, 

 and distinctly continuous therewith; whereas in the primary 

 rod the extra-coelomic piece (subepithelial) is thinner, and, 

 owing to the greater development of the coelom here, is more 

 widely separated from the rest of the rod. This suggestion 

 occurred to me forcibly in examining the connections of the 

 synapticula with the two bars. 



In a lucky series of sections, cutting the bars very accu- 

 rately transversely, one often gets the whole synapticulum 

 in sections, passing from one primary bar to the next, and 

 showing the connection of the rod in the transverse bar with 

 those of the main bars (fig. 31). Starting with the tongue 

 bar (T.), the rod forks, so that its contained cavity is no longer 

 bounded by a chitinoid wall ; one branch of the fork passes 

 towards each of the adjacent primary bars, and is con- 

 tinuous, not with the main part of the rod itself, but with 



1 Spengel gives a figure very similar to this one in pi. xvii, fig. 13, illus- 

 trating bis paper. 



