102 MORPHOLOGICAL DEVELOPMENT. 



pendent individual. Sir J. G. Dalyell found that in some 

 cases numerous fragments artificially separated, grew into 

 perfect animals.* In these creatures which thus remind us 

 of the lowest Hydrozoa in their powers of agamogenetic 

 multiplication, the individuals produced one from another 

 do not continue connected. As the young ones laterally 

 budded-off by the Hydra separate when complete, so do the 

 young ones longitudinally budded-off by the Planaria. 

 Fig. 166 indicates this. But there are allied types which 

 show us a more or less persistent union of homologous parts, 

 or individuals, similarly arising by longitudinal gemmation, f 

 The cestoid Entozoa furnish illustrations. Without dwelling 

 on the fact that each segment of a Tcenia, like each separate 

 Planaria, is an independent hermaphrodite; and without 

 specifying the sundry common structural traits which add 

 probability to the suspicion that there is some kinship be- 

 tween the individuals of the one order and the segments of 

 the other; it will suffice to point out that the two types are 

 so far allied as to demand their union under the same sub- 

 class title. And recognizing this kinship, we see significance 

 in the fact that in the one case the longitudinally-produced 

 gemmaa separate as complete individuals, and in the other 

 continue united as segments in smaller or larger numbers 

 and for shorter or longer periods. In Tcenia ecliinococcus, 



* Recently Mr T. H. Morgan has made elaborate experiments which 

 show that Planaria Maculata may be cut into many pieces from various 

 parts and of various shapes even a slice out of the side and each, if not 

 too small, will produce a perfect animal. 



t Since this was written in 1865 there has come to light evidence more 

 completely to the point than any at that time known. In the subdivision of 

 Plaiyhelminthes known as Turbellaria, there are some, the Microatomida 

 which, by a process of segmentation form "chains of 4, then 8, then 16, and 

 sometimes even 32 individuals." "Each forms a mouth [lateral] and for 

 some time the chain persists, but the individuals ultimately become sexually 

 matured and then separate." (Shipley, Zoology of the Invertebrata, p. 92.) 

 Here it should be remarked that the lateral mouths enable the members of 

 a string to feed separately, and that nutrition not being interfered with they 

 doubtless gain some advantage by temporary maintenance of their union 

 probably in creeping. 



