MUSEUM OF COMPARATIVE ZOOLOGY. 571 



As was to have been expected, the events of maturation in Heteropoda show 

 a greater resemblance to those in Limax than either of the other groups. 



The author withholds judgment as to whether the limiting layer of the ovule 

 is in this instance a true membrane, since he has not satisfied himself experi- 

 mentally of its physical and chemical properties. In young ovules it has the 

 aspect of a membrane, but its internal contour becomes less distinct in those 

 that are mature. Whether it is resorbed or mingled anew with the vitelline 

 sarcode, it does not exist after the exclusion of the egg. The nucleus of the 

 egg at the time of deposit is identical with the nucleus of the ovule (i. e. ger- 

 minative vesicle). It then appears in the living egg as a clear spot at the 

 centre of the yolk, which soon vanishes, and the central part of the vitellus 

 then assumes a more homogeneous aspect, in which, however, a radial figure is 

 discernible. In about half an hour there appears on one side of the yolk a 

 clear space resting with a broad base at the surface, and continuing toward the 

 centre in the form of a cone. It is composed of protoplasm without any 

 " protolecith." As it increases in size, the lecithic globules, especially near the 

 surface, take on a radial arrangement about the centre of the clear space. In 

 an hour and a half the protuberance of the first polar globule appears, and 

 within it one can distinguish the bipolar filaments and their enlargements 

 without the use of reagents. Two hours and thi'ee quarters after exclusion 

 the first globule is entirely detached, and the radial arrangement of the 

 "lecith" indicates the formation of the second amphiaster ; at this moment 

 there appears a voluminous protuberance at the nutritive pole, composed of 

 protolecith and sarcode. The superficial layer of the latter is here thicker 

 than over the other parts of the yolk. At the end of three and a half hours 

 the second globule is fully detached, and the vitelline protuberance has mean- 

 time entirely disappeared. Prolongations often seen arising from the surface 

 of this protuberance (PI. VIII. Fig. 9) are trabeculse resulting from the retrac- 

 tion of the albumen of the coagulated egg, and therefore do not pertain to the 

 vitellus,* Fol is unable to give any explanation of the meaning of this pro- 

 tuberance. — The metamorphosis of the germinative vesicle as shown by hard- 

 ened eggs confirms in many ways the views at which I had arrived. The 

 ve.jicle at the time of exclusion is still quite distinct, provided with a limiting 

 layer, and embraces a network of sarcodic filaments, but contains only a 

 few irregular refringent granules in place of a nucleolus. The enveloping 

 layer, the so-called membrane of the vesicle, becomes less distinct, although it 

 still remains visible. The vesicle diminishes a little in volume, but preserves 

 an almost spherical form, without shrivelling. At the opposite poles of this 

 great rounded cavity one now distinguishes two masses of granular substance, 



* It should be remarked in this connection, however, that the author subsequently 

 (page 112) alludes to this as a protuberance "with its accumulation of protoplasm 

 and sometimes pseudopods at its surface (PI. VIII. Fig. 9, Ev')." Since this is 

 the same figure as that cited in connection with the description given above, it would 

 appear that the author may have changed his opinion concerning these pointed ele- 

 vations between the times of the two writings. 



