4 W. T. CALMAN. 



the deeper parts of the colony are fouud scattered here aud 

 there a few small crystalline masses (PI. 1^ fig. 11). These 

 bodies dissolved somewhat slowly and without effervescence in 

 hydrochloric acid, but on account of their small number their 

 chemical nature could not be definitely ascertained, and they 

 cannot be certainly assumed to represent the stellate calcareous 

 spicules, e. g. of the Didemnidse. 



Scattered here and there in the test-substance are groups or 

 nests of rather large cells (PI, 1, fig. 10) containing rounded 

 deeply staining masses of varying size and appearance. The 

 protoplasm is often very granular, and no nucleus is visible. 

 It is possible that these obscure bodies represent the test- 

 phagocytes of Maurice, to which he ascribes the function of 

 absorbing the dead zooids, but it is to be noted that here they 

 do not occur in relation to the masses described above as 

 possibly representing degenerated zooids. 



General Conformation of the Ascidiozooids. 



The body (PI. 1, fig. 3) is divided into two regions, the 

 thorax and abdomen, united by a narrow neck. The thoracic 

 region contains the branchial sac, and varies in shape accord- 

 ing to the state of contraction. In the most expanded speci- 

 mens it is roughly square- shaped when seen from the side, aud 

 broadly oval in transverse section (PI. 2, fig. 14). A number 

 of longitudinal muscle-bands run in the mantle, about four to 

 six on each side. Along the ventral edge of the thorax runs 

 the large undulating endostyle. On the dorsal surface of the 

 animal is the wide atrial orifice, behind which is attached the 

 vesicle described below as probably representing an incubatory 

 pouch. In front of the atrial orifice is the very large atrial 

 languet. The languets belonging to the several zooids of a 

 system meet at their edges to form a composite roof to the 

 common cloacal chamber; seen from the outside this roof is 

 hidden by a continuation of the common test, in the centre of 

 which is the common cloacal opening. 



As a result of this arrangement, the individual languets are 

 somewhat irregular in shape. There appears to be no such 



