586 PROCEEDINGS OF THE AMERICAN ACADEMY. 



nection between nerves V and VI is illustrated in Figure 7. As has 

 been stated, a branch of left nerve IV sometimes anastomoses with 

 left nerve V in this region; left nerves VI and VII often show some form 

 of connection with it in the neighborhood of the ventral border of the 

 trunk muscles. Thus, with the slight connection sometimes occurring 

 between nerves II and III, a basis is formed for the band-like nerve 

 described by Hatschek ('92) as connecting nerves II-VII in this 

 region. Hatschek's Figure must be somewhat diagrammatic, 

 however, since this condition is found only on the left side, and even 

 here these connecting nerves are not constant in occurrence or size. 

 In nearly all cases left nerve V sends one or more branches to the velum. 

 These branches usually leave the ventral ramus near the ventral 

 border of the side muscles (Figs. 7, 8), and enter the velum on the left 

 side of the body. At least one of these branches forms an anastomosis 

 with a branch or branches of left nerve VI, and frequently a similar 

 anastomosis is formed with a branch or branches of left nerve VII. 

 These anastomoses vary greatly in character; it is often difficult to 

 determine the share of each nerve in the innervation of the velum. 

 This is especially true when, as sometimes happens, branches are 

 given off to the inner mouth plexus ventral to the anastomosis be- 

 tween branches of left nerves V and VI (Fig. 7). 



Nerve VI. — This ner\-e requires only a brief description. A form 

 of division of the trunk of this nerve in B. caribaeum may be noted in 

 Figure 6 (PI. 2). The dorsal rami of this nerve pair are similar to those 

 of the fifth pair of nerves; their main branches are illustrated in 

 Figures 6 and 7. The ventral ramus of the sixth nerve, both the right 

 and the left, is usually smaller than the corresponding ramus of nerve 

 V, but the cutaneous branches given off in its course over the trunk 

 muscles correspond to those leaving the similar portion of nerve V. 

 In both species the remaining branches of right nerve VI are distrib- 

 uted in the oral hood and external portion of the mouth border of the 

 right side. The ventral ramus of right nerve VI divides near the 

 ventral border of the trunk muscles into two or more slender branches, 

 which take a general course ventrad across the oral hood, and break 

 up into a portion of the outer mouth plexus. The corresponding 

 ramus of left nerve VI sends a similar branch, or branches, to the 

 outer plexus of the mouth border on the left side of the body. Left 

 nerve VI frequently sends a branch, or branches, to the inner plexus 

 on the left side of the mouth, but this is not uniformly the case. In 

 several specimens examined branches of left nerves III, IV, and V 

 formed the entire left portion of the inner mouth plexus. Heymans 



