262 



Prof. H. C. Bastian on Heterogenetic [Mar. 21, 



Just as in the previously described embryonal areas masses of different 

 sizes began to exhibit signs of change, so also here spherical portions of the 

 pellicle, differing within the limits above mentioned, began to undergo 

 other heterogenetic changes. This was first indicated by an increased re- 

 fractiveness of the area (especially when seen a little beyond the focal 

 distance) ; and almost simultaneously a condensation of its outer layer 

 appeared to take place, whereby the outline became sharply and evenly de- 

 fined*. At this stage an actual membrane was scarcely appreciable, and the 

 substance of the embryo (when examined at the right focal distance) 

 scarcely differed in appearance from the granular pellicle of which it pre- 

 viously formed part. 



So far as it could be ascertained, the individual embryos did not increase 

 in size, although they went through the following series of developmental 

 changes. The contained matter became rather more refractive, and the 

 number of granules within diminished considerably, whilst new particles 

 after a time seemed gradually to appear in what was now a mass of con- 

 tractile protoplasm. These new particles were at first sparingly scattered, 

 though as they were evolved they continued to grow into biscuit-shaped 

 bodies, which sometimes attained the size of yulToir "• x ^ s i zes were 

 distinguishable ; and many of them moved slowly amongst one another, 

 owing to the irregular contractions of the semifluid protoplasm in which 

 they were imbedded. Gradually the number of homogeneous biscuit-shaped 

 particles increased, and at last a large vacuole slowly appeared in some 

 portion of the embryo (fig. 8, b) ; it lasted for about half a minute, disappear- 

 ed, and then, after a similar interval, slowly reappeared. Much irregularity, 

 however, was observed in this respect. The next change that occurred was 

 the complete separation of the embryo from the cyst which it filled, and 

 the commencement of slow axial rotations. These rotations gradually 

 became more rapid, though they were not always in one direction. The 

 embryo became more and more densely filled with the large biscuit-shaped 

 particles (c) ; and at last the presence of cilia could be distinctly recognized 

 on one portion of the revolving embryo. Then, as M. Pouchet stated, the 

 movements grew more and more irregular and impulsive, so that after a time 

 the thin wall of the cyst was ruptured, and the embryo emerged as a 

 ciliated and somewhat pear-shaped sac provided with a large contractile 

 vesicle at its posterior extremity. 



Sometimes the embryo-mass at an early stage of its evolution divided 

 into two or four bodies, each of which developed within the cyst into a 

 perfect embryo ; and in place of exhibiting a regular rotation, they rolled 

 and tumbled over one another in the most irregular manner. On one oc- 

 casion I saw a cyst containing two embryos and four spherical Monads 

 about 5"jjW' m diameter, the latter having apparently resulted from the 

 * The first changes seem to take place rather rapidly, judging from the great diffi- 

 culty of recognizing the earlier stages. It was almost impossible to find an area which 

 was not already bounded by a delicate outer layer. 



