226 E. A. ANDREWS. 



From a side view (Fig. 1, 2, 3, 4) it extends forward ventrally 

 over the pre-oral chamber like a hood, with cirri like those of other 

 lancelets. These cirri, however, are perfectly smooth as shown in 

 Fig. 19 and do not present the denticulate outlines due to the 

 special sense organs found on the cirri of other Acraniata. The 

 number of cirri is 15 to 21, the small lateral, anterior ones being 

 involuted dorsally with the membrane and not seen from a ventral 

 view (Fig. 6). There may be a median cirrus and an equal number 

 of paired cirri on each side, as seen in the view of the macerated 

 skeleton (Fig. 24). Each cirrus is supported by a special carti- 

 lage-like rod springing from a common curved and jointed basal 

 arch, as in the common lancelet. Each rod, it will be observed, 

 springs from the distal end of one of the basal pieces composing 

 the common basis for all the rods. The hood differs from that of 

 the European form, and from that of the Florida form also, in 

 having the membrane continued up over nearly the whole length 

 of the cirri, leaving but their tips free. Moreover the median cirrus 

 is so long, and the most lateral so short that there is no reason to 

 doubt that the latter are the youngest as has been shown to be the 

 case in Amphioxus (27) although before the embryological facts were 

 known the examination of the adults had led Lankester (23) to the 

 opposite conclusion. 



If we were justified in regarding the lateral edges of the pre-oral 

 chamber as continuations of the metapleura, it is tempting to sup- 

 pose that the hood membrane, lying between those continued 

 metapleura and posteriorly continuous with the floor of the atrium 

 (Fig. 6) may be homologous with the sub-atrial ridges, may have 

 been originally an anterior continuation of those parts of the meta- 

 pleura which now unite posteriorly to form the floor of the atrium. 

 Such a view may be supported by the fact that in amphioxus, as 

 Willey has discovered (27), the oral hood arises from two beginnings 

 one right and one left : while other facts that militate against it may 

 be explained as secondary acquisitions connected with the remarka- 

 ble asymmetry of the oral region of the Acraniata. 



In addition to the above peculiar features of the reproductive 

 organs and fins, the Bahama lancelet presents some few minor ana- 

 tomical features which may now be described in comparison with 

 the similar structures in the European forms. 



