219 



BU)()d from tliL' anterior portion ol tlif iio(l\- and tiiu sinuses mentioned aljo\'e is 

 gathered by a system of afferent branchial veins, consisting (Sigerfoos, 1908) anteriorly 

 of two vessels, which fuse in the region of the visceral ganglion to form a single large 

 afferent branchial vein {a.h.v., figs. 77 and 79). This vessel extends posteriorly, occupy- 

 ing a median position between two gills. From it blood passes into the gill filaments, 

 where it becomes oxygenatetl and then passes into the paired efferent veins mentioned 

 above, which lead it once more to the auricles of the heart. Thus the circulation is 

 completed. 



This description of the circulatory system applies to Teredo navalis, and also, 

 according to Sigerfoos (1908), to Bankia opiddi. There is, further, according to the 

 statement of this author, an afferent renal \ein in the mantle, to the left of the epi- 

 branchial canal, which gathers blood from the posterior part of the bodN* and carries 

 it forward to the |ierine])hridial spaces at the posterior end of the kidneys. 



THE RESPIRATORY SYSTEM 



The greater portion of the length of Teredo is occupied b}' the gills. These consist 

 of paired lamellae which extend forward from the base of the siphons, di\iding the 

 mantle cavity into a ventral or infrabranchial cavity and a dorsal or siiprabranchial 

 cavity. The gill lamellae are made up of hundreds of transverse filaments, which are 

 fused at their bases and united at intervals for the remainder of their length by sup- 

 porting connectives or inter filamcn tar junctions. Thus the gills form a sort of trellis 

 work which permits a free passage of w-ater among the filaments. 



In cross section each gill resembles a letter V with the apex directed latero- 

 ventrally. Thus, taken together, the two gills in cross section roughly resemble the 

 letter W. If now a circle were placed about the W to represent a cross section of the 

 mantle of Teredo, the space below and to the sides of the W would represent the 

 infrabranchial cavity, and the space above the W the suprabranchial cavity. The 

 space included by the outer limbs of the W would be occupied by a structure known 

 as the gland of Desliayes, and by the intrapilamentar blood spaces. 



In typical forms, like Alya, the gill of each side consists of two V's, or a W. Siger- 

 foos (1908), from his observations on the developing teredinid larva, concluded that 

 the gills of Teredo correspond to the inner V of each gill of Mya, the outer member 

 never developing. 



OTHER ORG.\N SYSTEMS 



The nervous system of Teredo is essentially that of the usual lamellibranch type, 

 with modifications due principally to the elongation of the body of the animal. The 

 paired cerebral gaiiglia, lying just above and at each side of the mouth, are connected 

 by a long, narrow cerebral commissure. The pedal ganglion (p.g.. fig. 77), which lies 

 in the dorsal part of the foot, just below the oesophagus, is composed of two elements 

 morphologically which are closely fused into one. The pedal and cerebral ganglia are 

 connected by the usual cerebro-pcdal connectives, one on each side of the oesophagus. 

 The visceral ganglion, likewise composed of two major elements fused into one, lies 

 at the posterior end of the visceral mass, instead of under the posterior adductor 

 muscle as in the more typical eulamellibranchs. The visceral ganglion is connected 

 with the cerebral ganglia by a pair of cerebro-visceral connectives, which anteriorly 

 are widely separated, each occupying a lateral position just underneath the anterior 

 gills, but posteriorly approach each other and occupy a more nearly median position 

 as they pass through the visceral region. 



Just anterior to the visceral ganglion is a small ganglionic mass which has been 



