626 



INVERTEBRATE MORPHOLOGY. 



are persistent, are to be regarded as degenerate. Several 

 orders of Tuuicates may be recognized. 



1. Order Larvacea. 



To this order belongs the genus Appendicdaria which has 

 already been several times mentioned. It is throughout life 

 free-swimming and retains the larval tail, greatly resembling 

 in general appearance a tadpole larva. It secretes an exten- 

 sive test which is gelatinous in consistency and is but loosely 

 attached to the body, being frequently thrown off shortly 

 after its formation. The body (Fig. 285) is comparatively 



Pig. 285. — An Appbndiculaeian, Oikopleura cophocerca (after Foi from 



Hertwig). 

 a = anus. /= ciliated groove, 



c = notochord. g = brain with auditory vesicle. 



d' = pharynx. g' = first ganglion of tail. 



d" = stomach. h = testis. 



en = endostyle. ov = ovary. 



s = branchial cleft. 



small, the tail being attached to its ventral surface, while its 

 posterior extremity is somewhat enlarged and contains the 

 reproductive organs (ov and h). The branchial sac has but a 

 single pair of stigmata (s) which open to the exterior by a 

 pair of funnel-like tubes situated behind the anus. This ar- 

 rangement represents exactly a condition present in the larvse 

 of other Tunicates, two stigmata first forming and the atrial 

 sac arising as two separate invaginations of the body-wall 

 into which the primary stigmata open, the invaginations only 



