KUTCHIN. — PERIPHERAL NERVOUS SYSTEM OF AMPHIOXUS. 589 



C. Nerves of the Velum. 



The nerves of this structure have been so Httle described and 

 figured that they will be considered under a separate heading in this 

 paper. Rathke, as early as 1841, mentions the velum, giving the 

 number of tentacles as sixteen. Rolph ('76) notes that the velum 

 carries about ten cirri. Rohon ('82), van Wijhe ('93), and Hatschek 

 ('92) mention nerve branches passing to the velum; but the most 

 detailed description of the innervation of this structure is found in 

 the work of Heymans et van der Stricht ('98). These authors state 

 that the voluminous circular nerve of the velum is formed from 

 branches of left dorsal nerves IV, V, VI and VII, and appears to occupy 

 about the middle part of the sphincter muscle, at the interior of which 

 it gives off large branches. With regard to nerves passing to the 

 velar tentacles, these authors state (p. 36): "nous avons egalement 

 observe a I'interieur des tentacules des fibres nerveuses que nous 

 avons pu poursuivre jusque entre des cellules epitheliales." Contrary 

 to van Wijhe, they found in their preparations no impregnation of 

 sense cells in the velum. As mentioned in the discussion of nerve IV, 

 Heymans et van der Stricht describe a posterior branch of left dorsal 

 nerve IV which passes under the body of Hatschek, and reaches the 

 right portion of the velum. These authors illustrate (PI. VI, Fig. 22) 

 the large nerve branches passing to the velum, and also its circular 

 nerve. Dogiel ( : 02) finds branches from left nerves IV, V, VI, VII, 

 and even VIII and IX, taking part in the innervation of. the velum. 

 The branches of nerves IV and V are usually, however, most important. 

 Dogiel's enumeration of the more anterior nerves must be considered 

 in connection with this statement. This author shows (Taf. 20-21, 

 Fig. 13)* a portion of the plexus of the circular muscle of the velum. In 

 this figure branches of left nerves V, VI and VIII form the velar plexus. 

 In his Figur 1, branches from left nerves IV, V, VI and VIII pass to 

 the velum. The branches of nerves VIII and IX which he finds 

 occasionally passing to the velum are fine branchlets of the rami 

 viscerali of these nerves. 



My personal observations on the innervation of the velum were 

 made largely from dissected specimens of Branchiostoma lanceolatum 

 and B. caribaeum impregnated by the intra-vitam method with methy- 

 lene blue. Most of these specimens were fixed in ammonium picrate, 

 and preserved in a mixture of the ammonium picrate and glycerine. 

 A few specimens were fixed in ammonium molybdate, dissected and 

 mounted in balsam. In either case, a few drops of osmic acid added 



