590 SUMMAEY OF OUREENT RESEARCHES RELATING TO 



system of fine longitudinal or interstigmatic vessels is entirely want- 

 ing, so that the large vessels are not broken up into true stigmata." 

 All the species of this genus belong to the abyssal zone, and have an 

 exceedingly wide distribution, speaking to the uniformity of the 

 abyssal fauna. 



Organization of the Simple Ascidians.* — M. Ch. Julin describes 

 some structures which as yet have awaited the technical arts of modern 

 histologists. To put his results fairly, it will be necessary to consider, 

 with him, the position of the Tunicate group. 



After recapitulating the views of earlier naturalists, the author 

 expresses his agreement with Kowalevsky, Fol, and Gegenbaur, who 

 have insisted on the Vertebrate affinities of this class. He considers 

 that there is a ventral face, along the median line of which there runs 

 the endostyle or hypubranchial groove, and a dorsal which lies between 

 the oral and cloacal orifice. There is an anterior or oral orifice, and a 

 posterior or cloacal one. After a careful incision along the hypo- 

 branchial groove (directing the internal branchial cavity towards the 

 observer), it is seen (1) that the portion of the branchial cavity which 

 is characterized by the presence of the branchial clefts is distinctly 

 separated from the region near the buccal orifice by a circular swelling, 

 in which there lies a groove (the pericoroual groove of Lacaze-Duthicrs). 

 This pericoronal welt bounds posteriorly the coronal or buccal region, 

 in which there are inserted, in a circle, the tentacles. Along the 

 median doj'sal line there runs a fold, which is part of the wall of the 

 branchial cavity ; this is the dorsal raphe (posterior rajihe of Lacaze- 

 Duthiers). Near the anterior extremity of this raphe we see the 

 anterior tubercle or vibratile organ. The cloaca is placed between 

 the wall of the body and that of the branchial sac, and extends for- 

 wards as far as the pericoronal groove, and ventrally as far as the 

 hypobranchial groove. Between the two halves of the peribranchial 

 cavity there lies the interoscular region. (2) In the jiericoronal welt 

 there are to be distinguished an internal and an external lip. I'he 

 former is a membranous and completely circular fold ; the latter is 

 also membranous at its side, but disappears ventrally and dorsally. 

 (3) The anterior part of the dorsal raphe forms a swelling which is 

 closely connected with the surface of the body, and is marked by a 

 distinct groove — the epibranchial groove ; the posterior part of the 

 dorsal raphe is less projecting, and forms a membranous fold varying 

 in character. (4) Along the median dorsal line, and in front of the 

 inner lip of the pericoronal groove, there is a special organ, to which 

 its finder, Saviguy, gave the name of anterior tubercle ; others have 

 since called it the vibratile organ. The present author prefers the 

 former of these, so far as the term tubercle is concerned ; but as he 

 regards it as homologous to the cerebral hypophysis in the Vertebrata, 

 he prefers to speak of it as the hypophysial tubercle. In its interior 

 there is an infundibuliform cavity, the base of which is anterior ; it is 

 flattened from above downwards, and opens on the surface of the 

 tubercle by an orifice, the form of which is difierent in various 

 species. 



* Arch, lie Biol., ii. (1881) pp. 59-127 (4 pis.). 



