A STUDY IN MORPHOLOGY. 99 



serially homologous organs do not necessarily owe their resemblances to inheritance 

 from the unspecialisecl organs of a remote ancestor, and I think that the presence of a 

 distinct occular segment in Squilla compels us to recognise an homology between the 

 stalked eye and an ordinary appendage, although it is no doubt true that all the 

 groups in which stalked eyes occur cannot be traced back to a common stalked-eyed 

 ancestor, and also true that the stalked eyes themselves cannot be traced back to 

 ordinary appendages. 



The ocellus. 

 This is present from the first Nauplius stage to the end of the Schizopod series. 



Explanation of Table I. 



This table is designed to show at a single view the condition of each appendage at 

 each stage of development. 



For convenience I have included the compound eyes, the ocellus, and the labrum, 

 but do not wish to imply that these structures are or are not homologous with ordinary 

 appendages, and I have omitted the metastoma, although I have no doubt that this 

 should be included in a list of the appendages. 



In the table the word " same " indicates that the condition of the appendage is the 

 same as it was at an earlier stage, and does not refer to other appendages in the same 

 vertical line. 



