1880. } Development of Amphioxus lanceolatus. 77 
muscle plates in a single row, along either side of the animal. Each 
body consists of a case or capsule enclosing a central solid portion 
or matrix, within which are developed the generative products, and 
each case is placed with the center of its upper border in juxta- 
position to the line of overlapping or junction of two of the mus- 
cle plates (Fig. 6 a, PI. 11). Ordinarily these cases are small and 
inconspicuous, and lie entirely below the outline of the body 
muscles, but in the female, towards the breeding season, the ova 
increase so much in size that the cases become large and notice- 
able, closely pressed together, and extend for about a quarter or 
third of their diameter above the edge of the muscles to which 
they are attached, thus occupying a goodly share of the sides of 
the branchium. In the female which was in my possession there 
were twenty-six of these cases upon each side, extending from a 
little in front of the middle of the pharynx back to very near the 
branchiopore, In the males there were respectively twenty-three ` 
and twenty-five pairs of cases so that it is probable that there is 
no great difference in the number of pairs of cases in the two sexes, 
These generative organs are without outlets, the germinal products- 
escaping from them, when fully ripe, by the dehiscence or burst- 
ing of the walls of the capsule and the lining membrane of the cav- 
ity, and thus get into the branchium from whence they pass into the 
Surrounding water, the spermatozoa to come in contact with and © 
impregnate the ova, and the ova to develop into young animals. __ 
This escape from the body is probably effected during the 
feeding time of the animals, when there is a current more or less _ 
Strong passing through the branchium. The exact method by — 
which the ova become impregnated is not known, but it may be 
supposed that the spermatozoa, after passing from the male, move __ 
about in the water until swallowed by a feeding female, when they 3 
pass into the branchium with the greater quantity of the water, 
and so get to the cases containing the ova, penetrate the capsules, 
or more likely adhere to the exterior until the ova are extruded, 
and then effect the work of impregnation. Any ova which were 
in the branchium at the time of the entrance of the spermatozoa, es 
-and which had been recently separated from the cases, would of 
course be very quickly fastened upon and impregnated.) Each 
ovary, if a single case may be considered to represent an ovary, 
Contains from twenty-five to thirty ova, and each ovum is enclosec 
? eS, 18 possible that it may be shown hereafter that the ova are impres nae 
: < ter they pass from the female into the surrounding water, there meeti ting the fic 
Spermatozoa | which have been cients: from. me male, 
