GENERAL CONSIDERATIONS. 59 



nothing is known. We have further seen above (p. 37) that this 

 polypide develops in the primary zooecium exactly as the polypides 

 regenerate in those zooecia of the colony in which a previous 

 polypide has degenerated. 



In both cases, as it appears to us, the continuity of the individual 

 is retained by means of the persistent zooecium. We shall therefore 

 have to regard the rise of the primary zooecium from the larva 

 merely as metamorphosis, and to consider the newly-formed polypide 

 as a part of the same individual which is represented by the larva. 

 The cephalic section has been, if we may so express it, regenerated 

 in the attached larva. It would be theoretically inaccurate to regard 

 the rise of the polypide in the primary zooecium as the budding of a 

 new individual. We must here bear in mind that in the Phoronid 

 larva also it is chiefly the organs of the cephalic region that are 

 thrown off and regenerated during metamorphosis. 



The metamorphosis of the Ectoprocta is, indeed, connected with so 

 far-reaching a disintegration of the larval organs that it is not 

 possible to institute a direct comparison between the position of 

 the organs in the larva and in the adult. There is a gap here which 

 may be filled up by an examination of the metamorphosis of Phoronis. 

 We may in consequence assume for the adult individuals of the 

 Bryozoan colonies also, that the short line between mouth and anus 

 is the dorsal middle line, and that the ganglion lying at this part 

 represents the supra-oesophageal ganglion which is derived from the 

 neural plate. 



A few remarks as to the Bryozoan larvae in general have still to 

 be added. A comparison with the Actinotrocha is here specially 

 instructive. The Actinotrocha leaves the egg when only slightly 

 developed it feeds and grows considerably, and during larval life 

 develops the rudiments of many important organs (and this is also 

 the case in Cyphonautes). The Actinotrocha thus passes through 

 important processes of growth and development, and at the same 

 time seeks out a suitable point for fixation, and facilitates the dis- 

 tribution of the individuals over a large area. The swarming stage 

 of most Bryozoa, on the contrary, serves, as a rule, merely for 

 the last purpose. The larva does not feed, and consequently, the 

 alimentary canal degenerates. Its one office is to seek out a suitable 

 point of attachment, and for this purpose it is provided with a 

 highly-developed locomotory apparatus and sensory organs. So as 

 to facilitate locomotion as much as possible, the rudiments of the 

 future parts of the body are present in an invaginated condition only 



