BUDDING OF THE DIDEMNIDAE AND THE DIPLOSOMIDAE. 459 



individuals are arranged in such a way that their atrial apertures turn towards 

 each other. In this way commences the union of the individuals round a 

 common cloaca (KROHN, No. 63). This young tetrazooid colony shows con- 

 siderable resemblance to the youngest Pyrosoma colonies. The individuals 

 which are produced later by budding are always given off by the parent 

 laterally, and thus oc'cupy the spaces between the parent-individuals. They 

 t heinselves are very soon capable of multiplying in their turn. The daughter- 

 individuals at first lie somewhat away from the common cloaca, towards which 

 they only shift later. Systems consisting of two concentric cycles may thus 

 develop, the inner cycle containing the parent-individuals and the outer the 

 daughter-individuals. While the latter shift to positions round the common 

 cloaca, the individuals of the inner cycle disintegrate (JOURDAIN). The 

 common cloaca is nothing more than a pit-like depression of the outer surface 

 of the common cellulose mantle. This is also the case with the common 

 cloaca in Pyrosoma (cf. p. 403). 



New circular systems are produced in the Botryllidac, when one of the buds 

 belonging to a cycle does not shift towards the common cloaca, but moves 

 away from it. This individual, by reproducing itself through budding, 

 becomes the founder of a new cycle. 



D. Budding of the Didemnidae and the Diplosomidae. 



The conditions of budding in the families of the Didemnidae and 

 the 1 Di/ilosomidae are very peculiar. Since, in these families, the 

 buds remain connected with the parent until fully developed, re- 

 markable double individuals are produced which long since attracted 

 the attention of zoologists. Since, further, in the Diplosomidav, the 

 first budding process takes place during larval life, free-swimming 

 and still caudate larvae are found in which two branchial sacs are 

 well developed. On closer inspection, it is not difficult to distinguish 

 the branchial sac of the larva from that of the bud. In the brain of 

 the primary individual, moreover, the larval sensory organ can be 

 recognised, while in the bud it is wanting. 



Budding, in these two families, follows the type defined by GIAED 

 (No. 57) as " bourgeonnement pylorique." According to GEQENBAUR, 

 GANIN (No. 55), DELLA VALLE (No. 68) and other authors who have 

 investigated this method of budding, the newly formed individual 

 here arises through the concrescence of two originally distinct buds 

 (Fig. 85), one of which (the thoracic bud, k') yields the branchial 

 region with its organs, the peri branchial sacs, and the pharynx, while 

 the other (the abdominal hud, k) gives rise to the intestinal loop, the 

 genital organs and the heart. The first rudiment of the abdominal 

 bud (Fig. 232 A, k) is found as an outgrowth of the oesophagus of 

 the parent ; the thoracic bud, on the contrary (k') lies further down 

 on a level with the stomach, on the right side of the b(xiy and, 



