532 Mr. W. S. Macleay's Anatomical Observations 



forming an internal tunic corresponding to the outer covering 

 or test, and provided like it with two openings, as in having 

 branchiae which occupy all, or at least part of the membrana- 

 ceous cavity formed by the internal sides of the mantle. From 

 the Acrita they differ in having distinct nervous and generative 

 systems, while their intestinal canal is provided with two open- 

 ings both internal. 



This osculant group may be divided as follows : 



TUNICATA. 



Aberrant group ? 

 1. Tethya. 

 Or such Tunicaia as -have 

 their mantle adhering to 

 the envelope or test only 

 at their orifices; — their 

 branchiae regular, consti- 

 tuting the sides of the re- ■< 

 spiratory cavity; and their 

 branchial orifice surround- 

 ed by a membranaceous 

 ring, which in general is 

 supplied with tentacula, 

 as in Polypes 



Famities. 



"1. ASCIDID**. 



Telhyes simples Sav. 



BOTRYLLID*. 

 Teth. composies Sav. 



3. Lucid*. 

 Lucks Sav. 



Normal group f 

 2. Thalida, 

 Or such Tunicata as have 

 their mantle adhering 

 every where to the enve- 

 lope; their branchiae irre- 

 gular, consisting of two fo- "*■ 

 liated processes attached 

 to the sides of the thorax ; 

 and their branchial orifice 

 merely provided with a 

 valvule 



'4. BiPHORIDX. 



Animals. Generic Types. 



Simple and fixed, having 

 their orifices externally 

 irregular Ascidia. 



Compound and fixed, hav- 

 ing their orifices exter- 

 nally regular Poltclinum. 



Compound and floating, 

 having their branchial 

 cavity open at the two 

 extremities Pyrosoma. 



Aggregated in theiryoimg 

 state, and floating .... Salpa. 



•••»*•• 



•«••«• 



The 



* De Blainville considers that the Pyura Molina makes the passage from the simple 

 to tlie compound Tethya; that is, from the Ascidida to the Botryllida. Savigny 



shows 



