210 NIKOLAS KLEINENBERG. 



slightly refractive, and holding in suspension the egg, and 

 near it two or three polar globules — protoplasmic corpuscles 

 containing one or more large vacuoles. The egg itself is 

 an ellipsoidal body, whose normal axes measure about 0-14 

 and 0"10 mm. Its protoplasm is Avithout vitelline corpuscles, 

 and is therefore pale and transparent ; it is divided, as in so 

 many other eggs, into two substances : one, more compact and 

 with fine granules, is disposed in a network, or rather in the 

 form of a sponge, with relatively large spaces ; the other is a 

 clear, uniform, albuminous liquid, which fills the spaces. On 

 the surface the protoplasm is somewhat condensed, so as to 

 form a very thin cortical stratum. 



The two hemispherical blastomeres sometimes fit them- 

 selves with their plane surfaces so perfectly in contact that 

 it is impossible to separate them. Sometimes the centres of the 

 planes of contact become slightly excavated, and so separate, 

 leaving between them a central lentiform space, while the 

 margins still remain firmly adherent. This space might be 

 called the beginning of the segmentation cavity, if the changes 

 in form of the blastomeres did not soon make it disappear. 

 In fact, after a short period of rest, a tendency arises in each 

 blastomere to assume the spherical form, by which the peri- 

 pher^s of their respective bases are drawn towards the 

 corresponding centres, and becoming curved separate from 

 one another, so that finally they touch only at a single point, 

 in the place where the lentiform cavity formerly existed. 



The first two blastomeres at one time show distinct nuclei ; 

 at another are deprived of them ; at another show with great 

 clearness those stellate or radiating or fusiform groups of 

 fine granules, which the beautiful researches of the last few 

 years have shown to be phenomena constantly accompanying 

 the formation of new cells. 



The process of segmentation of the eggs of L. trapezoides 

 does not proceed in so simple and orderly a way as in many 

 other animals, and in not a few of the Annelids ; soon 

 begins a series of alterations in shape and position, of divi- 

 sions and buddings, of increasings and diminishings of 

 volume of the single cells, which altogether make it very 

 difficult to trace the type of this most important process, 

 which, as the first manifestation of the formative forces 

 hidden under the apparent sameness of the protoplasm, 

 serves as a beginning for the building up of the complicated 

 and definitely disposed structure of the body. 



After the division into two hemispheres a stage is often 

 observed in which the egg is composed of three blastomeres, 

 arranged in the form of a triangle, already described by 



