THE DEVELOPMENT OF THE EARTH-WORM. 213 



placed towards the centre we have a new form of the egg, 

 which no longer shows any trace of the arrangement which 

 preceded it. It is now a little spherical bladder, sometimes, 

 as far as can be seen, perfectly closed ; sometimes furnished 

 with a small opening, whose walls consist of a single layer 

 of cells, which vary considerably in length. About one pole 

 the cells are longer than they are broad, while at the oppo- 

 site pole the wall of the segmentation cavity is composed of 

 a series of cells, whose length is half that of the others or 

 less. There is not, however, a distinct boundary between 

 these two kinds of cells ; they rather pass the one into the 

 other by numerous gradations. There is not even a differ- 

 ence in the protoplasm ; in all it is uniform and finely 

 granular, since the reticular arrangement of the protoplasm 

 of the egg and primary blastomeres has already disappeared 

 some time ; each cell now nearly always contains a very dis- 

 tinct nucleus, whose volume varies with that of the cell. 

 The egg in this manner is transformed into a germinal 

 bladder, consisting of a single layer of cells of different 

 length, surrounding a somewhat large eccentric cavity, which 

 opens — if not always, certainly in some cases — by a narrow 

 opening (PI. IX, fig. 2). 



After this the reproductive activity is most marked in the 

 flat cells at one pole of the egg ; they increase in number, 

 become longer and push into the segmentation cavity, pushing 

 through its aperture or making their way between 

 the neighbouring loosely connected cells. But at the other 

 pole small cells detach themselves from the central extremi- 

 ties of the long blastomeres ; in this manner the segmentation 

 cavity, restricted on all sides, disappears, and the egg becomes 

 a solid and compact multicellular sphere. 



I shall, perhaps, have wearied the reader with the minute 

 description of the succession of changes, which, nevertheless 

 ^Z still remains somewhat unintelligible in consequence of the 

 scarcity of illustrations. But the importance of the argu- 

 ment and the divergence existing between my results and 

 those of such an excellent observer as Kowalewsky,must be 

 my excuse for the detailed nature of the account I have 

 given. Accordiug to the author above cited, the first phases 

 of development in L. agricola are very simple and regular. 

 The segmentation produces almost from the first cells of 

 of equal size, and a disc-shaped body is formed, which be- 

 comes divided by a fissure, representing the segmentation 

 cavity, into two laminae, each consisting of a single layer of 

 cells ; these soon become distinguishable by the nature of 

 their protoplasm, The circumference then raising itself 



