ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 943 



of the adult, a mass which lies ventral and posterior to it, and is composed 

 of very large ganglion-cells with very distinct nuclei and nerve-fibres ; 

 from the latter a nerve-cord passes ofi" into the tail, and on one side of it 

 there is a hollow sense-vesicle which has thin anterior and thick posterior 

 walls ; the unpaired eye is imbedded in the antero-dorsal angle of the wall, 

 and the otolith is situated on its floor, and projects upwards into its 

 cavity. This last is the only part of the nervous system which is hollow 

 at this time. The ciliated pit opens into the solid nervous substance at 

 about the middle point of the ventral surface of the first portion, and on the 

 dorsal surface of the second. 



As the ciliated pit of the embryo Amarcecium is connected exclusively 

 with the brain, it seems probable that its original function was the aeration 

 of the brain (compare the Nemertinea), In Ascidia and Ciona, and pro- 

 bably most other simple Ascidians, the function of the pit is that of a duct 

 for the so-called hypoj)hysial gland, while in Clavellina it communicates 

 with the brain and probably aerates it, and also acts as a reservoir to carry 

 off the secretion of the gland ; or, in other words, has retained its primitive 

 while taking on its secondary function. The pit is probably homologous 

 with the hyi^ophysis of vertebrates, in which the pineal gland possibly 

 represents the dorsal continuation of the ciliated pit. 



Some notes on the anatomy of Cynthia complete the paper. 



Anatomy of Distaplia.* — M. F, Lahille describes the anatomy of the 

 genus Distaplia, which has hitherto received but scant attention, though 

 the form in question appears to be of some importance as a synthetic type. 



There are 6 buccal, and 4 cloacal lobes, the latter forming a long 

 tongue in the adult. Four rows of very long bars (tremas) are united 

 medianly by transverse anastomosing vessels. The latter support the 

 " inter-trematic " sinuses which much increase the respiratory surface. The 

 transverse vessels, which in the high Phlebobranchs form what are called 

 the ribs of second and third order, very rarely interrupt the bars in 

 Distaplia. They are formed from the fusion of bifurcating papilla) which 

 spring from the middle of each inter-trematic sinus. The transverse sinuses 

 are in their disposition intermediate between that of the Diplosomias and 

 that of the Aplidiae. 



The pericoronal groove (gouttiere) is homologous with the vibratile 

 arcs in Appendicularias and morphologically independent of the branchiae 

 in all Ascidians. Into it the vibratile oval organ opens, and two nerves 

 occur on the base of the groove. The tentacles, at first two, then four in 

 number, increase by the formation of four other pairs appearing on the 

 neural side. 



As in the Aplidife, the posterior portion of the branchia, to the side of 

 the oesophagus, gives origin to the two endodermic tubes. These are, 

 however, unequal and separate, do not involve heart or genital organs, and 

 exhibit several muscle bundles and an ectodermic epithelium. They dis- 

 charge the asexual multiplication, and correspond to stolon-tubes. Their 

 marked development affects the other organs. 



The intestinal gland is greatly developed, its ducts anastomose abund- 

 antly. It opens into a reservoir which communicates by a canal with the 

 stomach. There is a cloacal diverticulum for incubation. 



In all their characters the young forms are Diplosomidee, and the 

 Leptoclinidse connect them with Pyrosoma. The adults are Distomidse as 

 regards the position of their viscera, but in general structure Aplidiae. 



* Bull. Soc. d'Hist. Nat. Toulouse, xxi. (1887) pp. 30-3. 



c! Q 2 



