TUN 1C AT A. 



FIG. 770. 



1191 



Dlazona vlolacea, magnified. (After Savigny.) 



circumscription ; animals sometimes scat- 

 tered, sometimes arranged in a quincunx ; 

 branchial orifice circular, without distinct 

 rays ; anal orifice very minute and indistinct ; 

 abdominal viscera pushed up by the side of 

 the thorax. 



Genus Leptoclinum, Milne-Edwards. Com- 

 mon body sometimes coriaceous, sometimes 

 gelatinous, thin, sessile and incrusting ; sys- 

 tems few ; individuals arranged irregularly 

 around common cloacal cavities ; abdomen 

 peduncled, short, smaller than the thorax. 



The tribe Botryllina (Ics BotryUiens, Milne- 

 Edwards) comprises those compound Asci- 

 dians that are united in systems around common 

 excretory cavities or cloacae, and whose bodies 

 are not divided into a distinct thorax and 

 abdomen, the viscera being pushed forward 

 on the side of the branchial cavity, and form- 

 ing with the thorax an ovoid mass. 



Genus Butryllus, Gaertner ; synonyms, Al- 

 cyonium, Auct., Polycyclus, Lamarck. Com- 

 mon body gelatinous or cartilaginous, sessile 

 and incrusting ; systems numerous, pro- 

 minent, round or star- shaped, with central 

 cavities; individuals, six to twenty in each 

 system, lying horizontally with the vent far 

 from the branchial orifice; branchial orifice 

 simple (fig. 771.). 



Genus Botrylloides, Milne-Edwards. This 

 genus resembles the foregoing in most respects, 

 except that the stars formed by the systems 

 of animals are irregular and ramifying ; the 

 cloacae being prolonged into the common 

 mass as irregular internal channels, on each 

 side of which the individuals are placed in 

 linear series, instead of having a simple star- 

 like arrangement around the cloacae, as in 

 Botryttut. The animals of Botrylloides, more- 

 over, have a nearly vertical position, and their 

 orifices are closely approximate (Jig. 783.). 



We should perhaps also refer to the group 

 of the Bolryllidic, an obscure form, first no- 



ticed by Molina*, and subsequently named 

 Pyura by Blainville, and considered by the 

 latter to form a link between the simple and 

 compound Ascidians. M. Blainville gives the 

 following characteristics. 



Fig. 771. 



Botryllus vlofaceus. Two of the star-like systems, mag- 

 nified. (After Milne- Edwards.) 



a, a, common test ; b, b, t>, some of the branchial ori- 

 fices ; c, the common anal orifice of one of the systems. 



Genus Pyura, Blainville. A pyriform body, 

 with two small short tubes, occupying a cell 

 in the external envelope, and forming, by its 

 union with 10 to 12 individuals, a kind of poly- 

 morphous mass somewhat resembling honey- 

 comb, apparently without any external orifice. 



* Saggio sulla Tlistoria natnrale del Chili, 

 logna, 1782, 4to. 



4c 4- 



Bo- 



