LEPTOCARDII : CIRROSTOMI. — I. 



Class C — LEPTOCARDII. (The Lancelets.) 



Skeleton membrano-cartilaginous ; no brain ; no skull ; the noto- 

 chord persistent and extending to front of body ; no heart, its place 

 being taken by pulsating sinuses ; blood colorless ; respiratory cav- 

 ity confluent with cavity of abdomen ; gill slits in great number ; 

 the water expelled from an abdominal pore in front of vent ; no 

 jaws; the mouth inferior, slit-like, with cirri on each side. (Gr. 

 XeTTTos, thin ; Kap8ia, heart.) 



Order I. CIRROSTOMI. 



The single order of this class contains but a single family. (Lat., 

 cirrus, hair ; Gr. crrofia, mouth.) 



Family I. BRANCHIOSTOMATID^. (The 

 Lancelets.) 



Body elongate-lanceolate, compressed, naked, colorless, the fins 

 represented by a low fold which extends along the back around 

 the tail, past the vent, to the abdominal pore ; eye rudimentary ; 

 liver a blind sac of the simple intestine. One genus, with 5 or 

 6 species ; small, translucent creatures found imbedded in the 

 sand on warm coasts. These animals are highly interesting to 

 the anatomist as showing the vertebrate type in its simplest 

 condition. 



1. BRANCHIOSTOMA Costa. (Amphioxus Yarrell.) 

 (jSpdyxi^a, gills ; arofia, mouth.) 



1. B. caribaeum Sundevall. Lancelet. Muscular bands 

 (myocommas) 55 to 60 (37 -}- 14 -}- 9 =r 60) ; tail short ; extremi- 

 ties attenuate. (Otherwise as in the European B. lanceolatum, 

 which has 56 to 60 myocommas; 35 4- 12 -f 13 = 60). N. Y. to 

 S. A. buried in soft sand, locally abundant. (Name from Carib- 

 bean Sea.) 



