493 



äusserem Epithel einfach als Ectoderm aufzufassen sei, eine Ansicht, 

 ich mich vollständig ;i 

 Heidelberg, 30. Juli 1879. 



welcher ich mich vollständig anschliesse 



3. On early stages in the embryology of Limax campestris 1 ). 



By Kdw. L. Mark, Cambridge, Mass., U.S.A. 



Some of the results of studies on the early stages of Limax, pursued 

 during April and May 1877 and continued in August and »September 

 1878, may be briefly summarized as follows: 



1) In the earliest stage which has been studied, — soon after the 

 egg is laid, — the germinative vesicle has been metamorphosed into a 

 centrally situated spindle with stellate figures centering at each pole 

 (Archiamphiaster Whitman) . 



2) The fibres of this spindle (first maturation spindle) are not at 

 this time easily distinguished from the other radiating lines of the am- 

 phiaster. 



3) The rays of the two stellate figures are very numerous, not 

 granular, and merge at their central ends into a small, ill-defined, 

 homogeneous sphere («area«) . The diameter of each stellate figure is 

 about one third that of the yolk. 



4) The first maturation spindle assumes a radial position , its 

 fibres become more conspicuous than the rays of the stellate figures, 

 and a prominent zone of fibre-thickenings (Kernplatte) appears at the 

 equator. The outline of the superficial aster is more sharply marked 

 than that of the deeper figure. 



5) The spindle moves outward along the radius which it occupies, 

 the external aster thus causing a low broad elevation of the yolk sur- 

 face, and becoming itself somewhat flattened. The poles of the spindle 

 (especially the external) become differentiated into a highly refractive, 

 homogeneous, oval body of considerable size. 



6) The spindle continues to move outward until its external pole 

 comes very close to the surface of the yolk. The equatorial zone of 

 fibre-thickenings meantime divides into two lateral zones which move 

 rapidly toward the poles of the spindle, leaving interzonal fibres bet- 

 ween them. 



1) The following preliminary account was written early in January 1870 for the 

 Zoologischer Anzeiger, but owing to the author's inability to state where the paper 

 on which it is based would appear, it has been withheld until the present. 



The plates are now under way and the paper will appear at an early date in the 

 Bull, of the Museum of Comparative Zoology, Cambridge, or in the Proceedings of 

 the American Academy of Arts and Sciences. 



