ON THE DEVELOPMENT OF LINGULA ANATINA. 101 



h. Comparison of the Results. 



As we can see from the above table the early develop- 

 mental history of Brachiopoda has been studied only by Lacaze- 

 Duthiers, Kowalevsky, Moese and Shipley. The researches 

 of these authors, moreover, dealt with but little else than external 

 changes ; in fact Kowalevsky and Shipley appear to have been 

 the only investigators who have attacked the more intimate prob- 

 lems. And it must accordingly be evident that our knowledge 

 of the embryology of Brachiopoda is far from being ripe enough 

 to enable us to draw general conclusions either upon the scheme 

 of development or upon the affinities of this class. Attempts to 

 build genealogical trees out of the materials at hand have of 

 course been made, but the results are admitted to be wholly 

 tentative. As far, therefore, as the present studies are concerned, 

 I think, it will be best to confine my summary to a comparison 

 of the leading features of the development of Lingula with those 

 of other Brachiopods. 



Reviewing the early developmental characters of Lingula 

 we can justly conclude that they do not agree with those of any 

 Brachiopod hitherto studied. On the other hand, I would call 

 attention in this connection, to the striking resemblance in the 

 mode of cleavage up to the 32- cell stage of Lingula to some 

 species of Phylactolsemata. 



The next stage in the development of Lingula, that is, the 

 formation of a cœloblastula certainly resembles the conditions in 

 other Brachiopods. A comparison of the gastrula, however, cannot 

 be made, since this stage has been observed in but one other 

 form, Cistella. I think we can state with certainty that in 



