CHAPTERS ON EVOLUTION. 



animal series the observed phenomena of development occasionally 

 1 resent a singular resemblance to the primary process about to be 

 alluded to, and already named segmentation ; such resemblance 

 being inexplicable save on the supposition that in these lowest forms 

 the development of the higher is foreshadowed in dim outline. 



Take as an example the development of Magosphcera (Fig. 98, i), 

 a low form of marine animalcule found living on the Norwegian coast 

 by Haeckel. It resembles the familiar animalcule known as the 

 Amoeba; 'but' during the development of new beings the Mago- 

 sphaera asslimes a spherical form (2), within which a nucleus (a) and 

 nucleolus (b) give it the appearance of a veritable egg (compare 

 Fig. 87, i). Next in order succeeds a process remarkably like that 



known as " segmenta- 

 tion" in the eggs of 

 higher animals. In the 

 course of this process 

 the Magosphaera divides 

 (3, 4, 5), until a stage 

 resembling the " mul- 

 berry stage," or morula 

 (6), is attained. There- 

 after the outer surface 

 becomes ciliated, and, 

 liberated from its invest- 

 ment, the Magosphaera 

 swims freely (7) in the 

 sea. Soon this free- 

 swimming sphere breaks up into detached fragments of protoplasm, at 

 first ciliated (8), but finally assuming (9) the adult Magosphaera form 

 (i). In the well-defined groups of the animal world, ranging from 

 the zoophytes, corals, and their neighbours (Ccelenterate animals), 

 up to Vertebrates, including man himself, we are presented with a 

 marvellous likeness and an undoubted correspondence in the form 

 afld nature of the germ, and of the processes in virtue of which that 

 germ is started on its developmental journey. 



Next in order, we note the occurrence, in the developing eggs of 

 all animals, of that process to which the name segmentation has been 

 given. We have seen that the germ or egg of the sponge, equally with 

 that of the sea-squirt, lancelet, chick, and also with that of Mammalia, 

 or quadrupeds, exhibits this process of division. The egg, at first 

 single-celled, becomes in this way many-celled ; and the variations 

 observable in the process itself are but insignificant when contrasted 

 with the extraordinary uniformity in the broad outlines thus exhibited 

 by the eggs of all animals in their first stages, and in the changes pre- 

 paratory to^the outlining* of the '-future form. But the similarity be- 



FIG. 98. DEVELOPMENT OF A PROTOZOAN. 



