ACTIVITIES OF MESENCHYME IN CERTAIN 



LARVAE. 



CHARLES B. WILSON. 



In consideration of the attention which has recently been 

 given to a study of the phenomena of the living cell, the fol- 

 lowing observations may be found of some interest. They 

 were made during the summers of 1896 and 1897 upon mesen- 

 chyme cells in the larvae of certain species of molluscs and 

 nemerteans. 



Freshly laid eggs of the nudibranch mollusc Tergipes despec- 

 tus (?) were obtained and reared to the veliger stage. Both 

 egg and young embryo are nearly opaque, the gastrula invagi- 

 nation being distinguished only by a slight increase in the 

 density. But after the mantle has been formed and the shell 

 has been secreted, the veliger becomes perfectly transparent. 

 The delicate shell is as clear as the finest glass, and the whole 

 internal structure is now plainly visible. 



Mesenchyme cells appear very early in development. They 

 arise from large primitive endoderm cells at the posterior edge 

 of the blastopore in the ordinary way for gastropod molluscs, 

 and are set free in the segmentation cavity. At first they are 

 approximately spherical in shape, and float about freely in the 

 liquid which fills the cavity, but they soon begin to elongate, 

 and become spindle-shaped.. At this stage in their develop- 

 ment activities were observed which are probably analogous to 

 those described for the polar bodies of certain animals.^ 



Unfortunately, I did not have with me at the time an objec- 

 tive of sufficient power to bring out the finer protoplasmic 

 movements distinctly. Well-defined amoeboid changes of out- 

 line, however, could be plainly seen. The cell, as it moves 

 about in the liquid which fills the segmentation cavity, puts out 

 blunt pseudopodia-like processes. These change both their 



1 Andrews, E. A., " Some Activities of Polar Bodies," /o/uis Hopkins University 

 Circular. November, 1897. 



