ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 957 



separates a dorsal from a ventral cavity, in the former of which lie the 

 genital glands ; the ovary in front of the testis. As in other Ascidians 

 six regions can be distinguished in the alimentary tract. The vibratile 

 organ is only the expanded extremity of the larval nerve-cord. 



Simple Ascidians.* — M. L. Eoule who in former memoirs dealt 

 with the organization and distribution of the family Phallusiadse, of 

 which Ciona intestinalis was taken as the simplest type, and the 

 variations in the other genera compared with it, in the present paper 

 describes the family of the Cynthiadae, the characters of which are 

 given as follows: — The tunic is tough and opaque, and frequently 

 presenting a colour of its own, not including vacuolated cells such 

 as those found in the Phallusiada?. The siphonal apertures have 

 a quadrangular form when moderately open, and when shut have 

 the appearance of a cross. The branchia (pharynx) is provided with 

 large folds extending from one end to the other, but these folds are 

 not traversed by cross folds so as to form distinct " infundibula " 

 as in the Molgulida?. 



In some points the Cynthiada? form a transition between the more 

 simple Phallusiada? and the more complex Molgulida3; e g. the tentacles 

 are in some forms merely simple filaments, as in the first-named 

 family ; whereas, in others, they carry lateral and even branched 

 expansions, leading to the condition found in the Molgulida?. 



Again, the dorsal groove is present in some, though more reduced 

 than in the Phallusiada) ; but in others it is absent, as in the 

 Molgulida?. 



If the peribranchial cavity be traced through a series of forms, it 

 shows a progression from a simpler fas in Ciona and BJiopalona) to a 

 more complex arrangement in the remaining genera of the Phallusiada?, 

 the Cynthiada?, and the Molgulida?. In the succeeding chapters the 

 various organs are described in detail and compared in various forms ; 

 at the end of each chapter a resume is given, which is here reproduced. 



The body-wall of the family shows the same general disposition 

 and relation to the " branchia" as in the Phallusiada?. 



The epidermis is formed of a single layer of columnar cells, the 

 height of which exceeds the breadth. The dermis consists of 

 connective tissue limiting numerous blood-sinuses, and including 

 bundles of smooth muscular fibres. 



The siphons resemble those of Phallusiada? ; the fold of the tunic 

 lining them is armed with small chitinous teeth. 



The coronal tentacles are simple in Polycarpa and Styela, and aro 

 slightly branched in Cynthia and Microcosmus. 



The " dermal prolongations " or vessels of the tunic are similar 

 to those of the Phallusiada?. The branchia of Eurjyriopsis, one of 

 the Molgulida?, is described, and the structure of this organ in 

 Cynthiada? compared with it on the one hand, and with the Phallusiada) 

 on the other ; hence it is inferred that in the Cynthiada? the branchia 

 is more or less intermediate between these families. 



The " pericoronal groove " and " ventral raphe " resemble in 

 general these organs in the Phallusiada?. 



* Ami. Fci. Nat.— Zool., xx. (18SG) pp. 1-124 (4 pi.-.). 



