No. 3.] GROWTH AND METAMORPHOSIS OF TORiVAR/A. 435 



Trochosphere ; the terminal anus is found in typical Echinoderm 

 larvae ; the oesophagus is endodermal, the ectoderm and its 

 thickened bands are as in the Echinoderm larva, the origin of 

 the muscle cells from enteroccels is common to Tornaria and 

 Echinoderm larva, and also the wandering mesenchyme cells of 

 the oesophagus. Metschnikoff therefore includes in a group 

 Ambulacraria, the two sub-types Radiata (Echinoderm) and 

 Bilateralia (Enteropneusta), and the following section is most 

 significant. " Es erscheint mir wahrscheinlicher das Balano- 

 glossus eine modificirte Thierform reprasentirt, bei welcher die 

 Ausbildung des radiaren Bauplanes, resp. der mannigfalligen 

 Differenzirungen des Wassergefab systems, so wie der Cutis 

 ausgebleiben ist ; obwohl es natiirlich auch denkbar ware dass 

 Balanoglossus eine primitivere Form als die Echinodermen uns 

 darstelle. Meine meinung stiitze ich haupsachlich auf die 

 unpaare Bildung der Tornaria, weil die paarigen Blindschlauche 

 der Bipinnarien und Plutei primitiver escheinen." 



Fewkes records Tornaria from Newport, R.I., in 1888. He 

 found much younger individuals than did Agassiz, but belonging 

 to the same species. Two figures are given of these. The 

 youngest form is slightly younger than the earliest stage I 

 have figured, and has not yet formed the circular ciliated band. 

 He speaks of the anterior longitudinal band as divided into two 

 separate bands, but seemingly without having carefully studied 

 the structure of the apical plate. He describes on each side of 

 the youngest larva two branching structures which he believes 

 to be Nephridia like those in Polygordius. This is undoubtedly 

 a mistake, and probably may be accounted for by the presence 

 of wandering mesenchyme cells in the blastoccel. 



Bateson published in 1884 the first of his series of papers 

 dealing with the embryology of B. Kowalevski. The first three 

 parts dealt with the different stages of development, and a 

 fourth was devoted to a discussion of the ancestry of the Chor- 

 data. The embryo of B. Kozvalevski has a direct development 

 that is without a Tornaria stage. The blastula invaginates at 

 one pole (without formation of mesenchyme) to form a typical 

 gastrula, the blastopore ultimately closes at the point where 

 the anus subsequently opens. The archenteron gives off five 

 pouches, — a single large anterior pouch, the anterior enteroccel 

 which subsequently communicates with the exterior through a 



