120 A. H. L. NHWSTEAD. 



septum Kupffer described an orifice leading from the atrial 

 cavity to the perivisceral cavity, by means of which water could 

 penetrate the latter. He also described two orifices at the 

 bottom of the pharynx, one on each side of the posterior 

 groove which extends between the end of the endostyle and 

 the oesophageal opening ; these orifices he described as opening 

 into the atrial cavity. 



Roule (1), in his monograph on Ciona, gives a detailed 

 account of the relations of this cavity, which he calls '' la 

 cavite geuerale du corps," but does not mention any openings 

 into the atrial cavity or pharynx ; on the contrary, he denies 

 the existence of any possible communication between it and 

 the atrial cavity : " vers chacune de ces ouvertures [i. e. the 

 openings in the septum for the passage of the oesophagus, 

 rectum, &c.], la lame peritoneale, inseree sur tous les organes 

 qui la traversent, envoie entre eux de petits prolongements, de 

 telle sorte qu'il ne peut exister aucuue communication, si 

 minime qu'elle soit, entre la cavite peribranchiale et la cavite 

 generale" (p. 107). He considers the perivisceral cavity as 

 the remains of the primary blastocoele of the larva, which has 

 become reduced and, as it were, pushed back to the posterior 

 end of the body by the development of the atrial cavity. 



Van Beneden and Julin (2) discuss the question as to the 

 nature of this cavity ; they consider that it cannot be part of 

 the original blastocoele, since, according to the description of 

 the vascular system given both by Kupffer and Roule, it does 

 not communicate at all with that system. 



Two other possibilities remain : 



[a) It may be derived from the atrial cavity ; or 



[h] it may be derived from the pharynx. 



The latter view is considered by van Beneden and Julin to 

 be the more probable one; they suppose the perivisceral cavity 

 to be homologous with the epicardium described by them in 

 Clavellina. In " Popinion la plus probable, elle constitue une 

 dilatation de I'epicarde, auquel cas elle devrait communiquer 

 non pas avec les cavites peribranchiales, mais bien avec le sac 

 branchial Si I'espace perivisceral repond a la cavite epi- 



