NOTE ON THE CILIATED PIT OF ASCIDIANS. 137 



If the excretory function of the ciliated pit be merely 

 secondary no homology can exist between it and the pro- 

 boscis pore of Balanoglossus, 1 or the external opening of the 

 left anterior pouch from the fore-gut, described by Hatschek 2 

 in Amphioxus. 



It is more probably homologous with the hypophysis of 

 Vertebrates, the original functions of which may have been the 

 aeration of the brain. When a complete blood-supply to the 

 head was effected aeration by this means would no longer be 

 required, and since a definite and complete excretory system 

 had been at the same time developed, there would no longer 

 be any necessity for an excretory organ in this position. Thus 

 the hypophysis at the present time may represent merely a 

 rudimentary condition of the gland and ciliated pit in Ascidians, 

 having almost atrophied, and quite lost its function as a con- 

 sequence of the development of the ordinary Vertebrate 

 excretory system. 



It is possible that the pineal gland of Vertebrates may 

 represent the dorsal continuation of the ciliated pit in the 

 embryo Amarax:ium (fig. 3, E). 



THE ANATOMY OF CYNTHIA. 



Whilst investigating the condition of the ciliated pit in 

 various genera of Ascidians, I observed several features in 

 Cynthia, which, as far as I know, have not hitherto been 

 described. I have therfore thought it worth while to publish 

 a short account of the general anatomy and histology of the 

 species I have studied, which I believe to be Cynthia 

 rustica. 



N.B. — Some of the generic characters, in which the Cyn- 

 thiidse differ from the Molgulidae, have been pointed out by 



1 Bateson, W., "The Later Stages in the Development of Balanoglossus 

 Kowalevskii, &c," this Journal, 1885. 



2 Hatschek, B., " Studien iiber Eutwicklung des Amphioxus," 'Arbeiten 

 aus dem Zool. Inst. Wien,' 1882. 



