OF A REMARKABLE FORM OF COMPOUND TUNICATA. 375 



may be affirmed that, when the zooids of a compound genus are pedimculated on a central 

 axis, vascular continuity is the most striking characteristic ; hut, where they are immersed 

 in the connecting substance, the importance of vascular communication as a character 

 yields to the existence of a common cloacal system. The curiously modified forms of the 

 latter system, taken as one of the grounds of classification, I shall have to notice in a 

 summary of Australian genera, now in progress. 



It is now full time to give a name to the little subject of this paper ; an appropriate 

 one would be Diplosoma, as at once sufiiciently expressing the peculiar natui-e of the 

 animal. I therefore propose to call the species Diplosoma Mayneri, after Mr. F. M. Ray- 

 ner. Surgeon of H.M.S. ' Herald,' who investigated its anatomy with me, and satisfied 

 himself of the truth of the descriptive particulars above given. 



June 1858. 



EXPLANATION OF THE PLATE., , , - V^ ' 



Tab. LXV. Div. L . . i^^^M |<^P' 



Fig. 1. A diplozooid, separated from the mass, and highly magnified, exhibiting the more important 

 points of its structure. 



a. a. The two distinct thoraces. 



b. The pedicles, bearing gemmations near their confluence, and a caudal appendage at the upper 

 part of their dorsal surface. 



c. Branchial opening. 



d. Anal aperture. 



e. Visceral mass. 



/,/. Pallio-vascular tubules, with their dilated glandular extremities. 

 g. Stomach, showing a sort of valvular cardiac orifice. 



h. Ovarium, containing one principal ovum, and several others in an earlier stage of develop- 

 ment. 

 i. The large sacculated testis. 

 Fig. 2. Ovum in which the process of cleavage is going forward. 

 Fig. 3. Ovum further advanced. 

 Fig. 4. Primary state of the embryo, showing the central vitelline mass, the three sucker-tubes, and 



caudal process. 

 Fig. 5. Embryo in the ovum more fully developed, presenting, besides the frontal suckers and tail- 

 process, nearly all the parts discernible in the adult state. 



a. a. The two distinct thoraces. 



b. Otolithic sac, occurring only on one of the thoraces. 



c. The frontal suckers arising in common with 



d. The pallio-vascular processes from the pedicle of the thorax to the left. 



e. Vitelline mass, in which the viscera are faintly marked off. 

 /. The caudex. 



g. Polygonal cells of the primordial test. 

 Fig. 6. Cells and intercellular corpuscles of the connecting substance. 

 Fig. 7. Marginal coronet of the branchial opening. 



Fig. 8. Caudal process of the adult, springing just below the root of the endostyle. 

 Fig. 9. Caecal extremity of one of the stolons. 

 Fig. 10. Nervous ganglion with otolithic sac and eye-speck (?). 



