262 LECTURE XII. 



nients seemed to have been spontaneously cast off, and the embryos 

 escaped from the ruptured surface. Those at the lowest observed 

 staGje of development presented a roundish or oblong form with 

 feeble lateral indentations indicating two or three segments, a wide 

 alimentary canal filled with the yolk-mass, and no trace of antennas, 

 feet, eye-specks, or jaws. When the embryo has attained one line 

 in length, the segments are defined and increased in number to 

 twenty or thirty ; on the anterior half of these, commencing with 

 the third segment, the conical bases of the setigerous feet are de- 

 veloped; the segments appear to be increased in number by suc- 

 cessive divisions of the second; a pair of eye-specks and jaws are 

 next developed ; and the segments, being multiplied and provided 

 with single-bristled feet, the young Eunice presents the characters 

 of a Lumbrinereis of Audouin and Edwards. 



In most branchiated anellids the embryo is excluded as a ciliated 

 spheroidal animalcule. It lengthens, partially casts its cilia, retaining 

 them arranged either in a cincture round the middle of the body, or 

 in two bands one about each extremity. At the anterior end the eyes 

 or eye-specks appear ; the segments are indicated on the rest of the 

 body, and the tubular feet and their bristles sprout forth ; the little 

 anellid afterwards taking on the modifications which distinguish its 

 family, its genus, and, finally, its species. 



In the development of the typical Anellids, there is something, there- 

 fore, which merits the name of a metamorphosis. Professor Loven, 

 for example, captured, in August, on the shores of the Baltic Sea, a 

 discoid animalcule {Jig. Ill), which rapidly moved by means of two 

 rows of vibratile cilia : the principal row being situated upon a pro- 

 jecting ring {b\ at the margin of the disk. This ciliated body dif- 

 fered from the gemmules of the Polypi, in being provided with a 

 mouth (e) and an anus (c), the latter occupying the 

 apex of the cone. The course of the alimentary 

 canal, which extended from one to the other 

 aperture, was detected by feeding the little animal 

 with indigo. In a short time the cone began to 

 elongate and to be divided into segments, which 

 were developed in four parts, the two principal 

 pieces forming half-rings, one upon the ujjper, the 

 other upon the lower surface, which were united by 

 two shorter side-pieces. Coincident with the elon- 

 rt''''^SS<r gation and segmentation of the body, was the de- 



\, velopment of the head from the discoid surface (a\ 



tmbryo ol Nereis. ^ \ y 



upon which first the black ocelli, and then two 

 pointed filaments, or antennae (/), made their appearance. The 



