36 



PHYLUM TUNIC ATA (UROCHORDA). 



developed, or one part alone may develop, so that zooids may be found 

 with two sets of intestines. In such cases the old intestines disappear 

 and the phenomenon may be regarded as one of regeneration. 



Didemnum Sav., colony thick and fleshy, pharynx with three rows of 

 stigmata, most seas. Didemnoides v. Drasche. 

 Sarcodidemnoides Oka. Leptoclinum M. -Edw. , 

 colony thin and encrusting, 4 rows of stig- 

 mata. Tetradidemnum Delia Valle. Poly- 

 syncraton Nott. Eucoelium Sav., 6 rows of 

 stigmata, Med. and Red Sea. Hypurgon 

 Sollas, with faecal pellets included in the 

 test, Malay Peninsula. 



Fam. 5. Diplosomidae. Colony usually 

 thin, transparent and encrusting, usually 

 without spicules in the test, pharynx with 4 

 rows of stigmata ; body divided into thorax 

 and abdomen ; vas deferens not spirally 

 coiled ; gemmation* as in the Didemnidae : 

 the larva produces a well-developed bud be- 

 fore fixation. Diplosoma Macdonald, Med., 

 Atl., Pac., Austr. Diplosomoides Herd., with 

 spicules, Med. Brevistellium Jourdain. As- 

 tellium Giard. Pseudodidemnum Giard. 



Fam. 6. Coeloeormidae. Colony massive, 

 deeply concave on upper surface, not at- 

 tached ; zooids large, scattered all over the 

 surface, mouth .Vlobed ; test soft with cal- 

 careous spicules near surface of 

 colony ; pharynx large, dorsal 

 lamina as languets ; intestine 

 extending behind pharynx but 

 not forming distinct abdomen ; 

 testis as pyriform vesicles which 

 join a spirally coiled vas de- 

 ferens. Coelocormus Herdman, 

 S. Atlantic, 600 fins. 



FIG. 29. A blastozooite of Clavelina, side view, 

 diagrammatic (after Delage and Herouard), 

 1 atrial aperture ; 2 subneural gland ; 3 mouth; 

 4, 5, epicardial tube ; 6 heart ; 7 stolon ; 8 sto- 

 lonic septum ; 9 stomach ; 10 ovary ; 11 testis ; 

 12 oesophagus ; 13 anus. 



* From the recent account of Pizon (Comptes Rendus, 137, 1903, p. 759) 

 which is somewhat condensed, the budding appears to be as follows : 

 The larva buds before fixation. Of the two individuals so formed, O 1 and 

 B 1 , the oozoid O 1 or zooid into which the larva itself develops buds a new 

 thorax (pharynx, oesophagus and rectum) and so becomes bithoracic. 

 After twenty-four hours the old thorax degenerates, while its abdomen 

 V 1 persists and retains its connection with the budded thorax. There is 

 thus formed a new individual O 2 , which in its turn produces two buds ; 

 from one of these proceeds a new thorax O 3 from the other a new abdomen 

 V 2 . After about twenty-four hours these separate in such a way that 

 the new thorax O 3 takes the old abdomen V 1 , while the thorax of O 2 keeps 

 the new abdomen V 2 . O 2 having thus acquired a new abdomen buds a 

 new thorax O 4 and then after twenty-four hours loses its old thorax. A 

 new zooid with the old abdomen V 2 and the new thorax O 4 is thus formed. 

 O 3 goes through the same series of changes as those described for O 2 ; i.e. 

 it first doubles itself and gives rise to two new zooids, of which that with 

 the old thorax O 3 becomes bithoracic and then loses its old thorax. The 

 zooid B 1 produced by the free larva behaves like O 2 . 



