CLEAVAGE IN TOXOPNEUSTES VARIEGATUS. 



145 



the gastrula from the archenteron, either during or after its 

 invagination, than with the idea of associating the primary 

 mesenchyme with an early differentiation in the segmenting egg. 

 The following table gives a resume of the more recent literature, 

 with the inclusion of Bury's observations of earlier date on 



Antedon. 



TABLE SHOWING TIME OF MESENCHYME FORMATION. 



It will be seen that among the Asteroidea there are some dif- 

 ferences between various forms in their methods of mesenchyme 

 formation. Field (1892) described these cells in Asterias vulgaris 

 as being given off from the developing archenteron even from the 

 beginning of its invagination. Gemmill (1914) found no mesen- 

 chyme cells in the normal larvae of Asterias rubens until gastrula- 

 tion was well advanced, when they appeared at the end of the 

 archenteron. MacBride (1896) found in Asterina gibbosa that 

 no mesenchyme was formed until after gastrulation was complete. 

 In connection with these accounts it is interesting to note the 

 results of Herbst (1896) who experimentally induced larva^ of 

 Asterias glacialis, which normally produce mesenchyme only 



