CHAP. IV.] THE VOYAGE HOME. 189 



or iinmediatelj after their extrusion ; tliat the first develop- 

 mental stages are run through rapidly ; and that the young are 

 passed back from the ovarial opening, which is at the side of the 

 mouth, along the dorsal ambulacra, and arranged in their places 

 by the automatic action of the ambulacral tentacles themselves. 



The very remarkable mode of reproduction of certain mem- 

 bers of all the recent classes of Echinodermata by tlie inter- 

 vention of a free-swimming bilaterally symmetrical " pseudem- 

 bryo " developed directly from the " morula," from which the 

 true young is subsequently produced by a process of internal 

 budding or rearrangement, has long been well known through 

 the labors of a host of observers headed and represented by the 

 late illustrious Professor Johannes Miiller, of Berlin. 



At the same time, it has all along been fully recognized that 

 reproduction through the medium of a pseudembryo is not the 

 only method observed in the class ; but that in several of the 

 Echinoderm orders, while in a certain sj^ecies a wonderfully 

 perfect and independent bilateral locomotive zooid may be pro- 

 duced, in very nearly allied species the young Echinoderm may 

 be developed immediately from the segmented yelk without 

 the formation of a pseudembryo, or, at all events, with no fur- 

 ther indication of its presence than certain obscure temporary 

 processes attached to the embryo, to which I have elsewhere 

 (Phil. Trans, for 1865, p. 517) given the name of " pseudem- 

 bryonic appendages." 



This direct mode of development has been described in IIolo- 

 thuria tremula by MM. Koren and Danielssen, in Synajptula 

 vivipara by Professor Oersted, in a " viviparous sea-urchin " by 

 Professor Grube, in Echinaster and in Pteraster by Professor 

 Sars, in Asteracanthion by Professor Sars, Professor Agassiz, 

 Dr. Busch, and myself, in Ophiolepis squamata by Professor 

 Max Schultze, and in a " viviparous ophiurid " by Professor 

 Krohn. I^o less than four of these observations were made on 

 the coast of Scandinavia. In temperate regions, where the 



