118 W. BLAXLAND BENHAM. 



Fig. 25. The rod has passed further into the subendostylar tissue, and 



lies above the corner of the coelom. 

 Fig. 26. The cavity of the rod communicates with the subendostylar 



ccelom most distinctly. 



Figs. 27 — 29. — Transverse sections of an abnormal primary bar at different 

 levels. 



Fig. 27. Section about the middle of the length of the bar. The epi- 

 thelium and general structure of the bar is normal, but contains three 

 separate primary rods, 1, 2, 3, each partially surrounded by a layer of 

 ccelomic epithelium, vise. v. The visceral blood-vessel, som. v. The 

 somatic blood-vessel, s.m. The very short septal membrane, cos. Coelom. 

 skel. V. Extra-coelomic skeletal blood-vessel. 



Fig. 28. A section of the same bar lower down. There are here only two 

 rods, partially fused ; the rod to the right is formed by the fusion of 

 rods 1 and 3 (in Fig. 27). 



Fig. 29. The same rod lower down, nearer the endostyle. The two rods 

 have separated again, but have shifted their relative positions. 



Fig. 30. — Three sections of a normal primary rod at different levels, {a) 

 Close to the endostyle, where it consists of two independent pieces, {b) Slightly 

 higher up, where a third piece (sometimes isolated) plugs the gap between 

 the two pieces, with which it is more or less fused, (c) The general condition, 

 in which the fusion of the three pieces is complete, except for a narrow axial 

 cleft (? or less refractive substance). R. The rod, in the usual sense, cu. 

 " Cutis," or outer wall of ccelom. cce. Coelom. skel. b. v. Skeletal blood-vessel. 

 som. V. Somatic vessel. (Cf. Figs, 13—16.) 



Fig. 31 a. — The connection of synapticulum with the primary and tongue 

 bars. The section is accurately transverse, and includes three bars and the 

 synapticulum. P^ P^. The two primary bars. T. The intervening tongue 

 bar. si/n. To the left, half a synapticulum cut along its whole length, and 

 continuous, as is seen, with one half of the tongue rod and the extra-coelomic 

 " cutis" (cm.) of the primary rod. si/n}, syn^. The two portions of the other half 

 of the synapticulum (the intervening portion is in a section not figured), h. »'. 

 The subepidermic skeletal blood-vessels of the primary bar. h. v^. The skeletal 

 vessel of the tongue bar, which is seen to divide into a right and a left branch, 

 which fall into b. v^. of the primary bars. cce. Ccelom of the primary bar. 



Fig. 31*. — The next section of the primary bar (P*) showing the passage 

 of syrfi. into the cutis (cm.). Other letters as in Fig. 31a. 



