342 E. W. MACBRIDE. 
and “ adult’? planes respectively. A rudiment of the przoral 
lobe of the larva is retained, as we shall see, until the close 
of the metamorphosis, and by means of it I found it possible 
to determine the direction of the “ larval” plane up till the 
adult form has been almost attained. Hence, by cutting 
sections parallel to the larval plane, one can follow the internal 
changes of the metamorphosis step by step; then when the 
metamorphosis is complete it is possible to correlate with less 
difficulty sections cut parallel to the two planes, and the 
further history may be followed via, so to speak, the adult 
plane. This was the course which I adopted; and I also 
penetrated back a considerable distance from the adult con- 
dition into the stages of the metamorphosis by sections parallel 
to the adult plane, and so confirmed results obtained by the 
other method. For the youngest stages of all, which are 
spherical, orientation is, of course, impossible, and one has to 
trust to chance to getting sections in the proper direction ; 
but it is fairly easy to recognise from their appearance when 
this is so. 
General Account of the Development. 
The ontogenetic history of the Asterina gibbosa may be 
conveniently divided into three parts: first, the development of 
the bilaterally symmetrical larva from the egg; second, the 
metamorphosis of this larva into the young star-fish ; and lastly, 
the gradual development of what we may term the young adult 
into the sexually mature form. I have made no observations 
on the segmentation of the egg, nor on the gastrulation; my 
work, properly speaking, commences with the completed 
gastrula, and my material was not suitable for observing the 
development of the calcareous plates. On all these points I 
intend, however, for the sake of completeness, to say a few 
words, and my authority will be Ludwig, who, in his classic 
research (12), has on these subjects left nothing to be desired in 
point of view of completeness. I may add also that the figures 
illustrating the changes in external form are copied from 
Ludwig’s memoir. The three figures illustrating the relations 
