8 H. H. NEWMAN. 



large vesicle (a posterior enterocoel pouch) present on the left side 

 only." Gemmill had described for Asterias rubens a pair of poste- 

 rior enterocoel pouches which seemed to play little part in the for- 

 mation of the posterior coeloms, but merely produced mesenchyme. 

 My own observations of the normal Patina larva enable me to con- 

 firm Gemmill's findings. More frequently than not two small 

 paired pouches, very thin-walled, appear at about the level of the 

 future stomach. Sometimes only one such pouch appears. The 

 pouch is never large nor thick-walled, as one might infer from 

 Heath's account. The nearest semblance to his structure is seen 

 in my Figs. 20 and 21, where the archenteron shows a unilateral 

 outpouching. Since this condition is relatively rare, however, one 

 can not lay much emphasis upon it. I was riot interested in fol- 

 lowing up the fate of any of these structures, but Heath promises 

 that an attempt will be made to determine their ultimate fate. 



On the basis of his observations on Patina, Heath allows him- 

 self to engage in rather far-reaching phylogenetic speculations and 

 sums up his position as follows : " I am strongly inclined to look 

 upon the anterior vesicle in Patina as the homologue of the pro- 

 boscis coelom of Balanoglossus, while the posterior outgrowth cor- 

 responds to the trunk ccelom and the intermediate pairs of vesicles- 

 in the echinoderms, often with two hydropores in certain species, 

 is the equivalent of the collar ccelom." In another place he says 

 that his discovery of the apical plate in Patina is a strong bit of 

 evidence in favor of the theory that the apical plate of the trocho- 

 phore larva and of the echinoderm larva are homologous struc- 

 tures. It may readily be seen that to the phylogenist these are 

 speculations of considerable moment, inasmuch as they seem to be 

 confirmatory of the rather current idea that there is more than a 

 superficial resemblance between the Tornaria larva of Balano- 

 glossus and the Bipennaria and Auricularia larvse of the starfishes 

 and sea-cucumbers. 



I have been persuaded to publish this correction of Heath's 

 account merely to avoid the strong probability of the error creeping 

 into our textbooks and becoming part of our permanent literature. 

 Many another error has been thus immortalized; for, once in a 

 textbook, a statement, no matter how erroneous, seems to be passed 

 from generation to generation. 



