OF PLANOCERA ELLIPTICA. 311 



The spermatic particles of Polycelis variabilis 1 have observed, but shall describe 

 them in connection with the development of its eggs on another occasion. Those of 

 Planocera elliptica have hitherto escaped my notice. Their description would have 

 been here in place. 



III. THE LAYING OF THE EGGS. 



The spawning period lasts from the middle of May to the middle June, setting aside 

 the precocity of some individuals, and the backwardness of some others. 



When the animal lays its eggs it creeps along the smooth surfaces of the submarine 

 bodies, either stones, pieces of wood, or sea-weeds, &c. It leaves behind it a thin band 

 of mucosity of the width of its body and in which the eggs are arranged in one layer, 

 side by side, in transversal rows (figs. 7 and 7 a). The eggs are ejected in certain 

 quantities, and maintained a while under the flat body of the animal, which secretes 

 the mucosity and gives to them this peculiar arrangement; a short time afterwards 

 the bands may be isolated from the surface upon which they were fixed, and the eggs 

 will remain in their respective places. They may be seen distinctly through the 

 transparent and hardened mucus, which now has the appearance of a thin leaf 

 of whitish glue. The length of the bands themselves varies considerably, as the 

 animal may be disturbed and compelled to recommence another one somewhat apart 

 from the first. Sometimes the interruption is so often repeated that instead of continu- 

 ous bands we have a series of irregular patches in which the linear arrangement of the 

 eggs is no longer observed (figs. 9 — II). This is particularly the case towards the 

 end of the laying; the animal appears uneasy, impatient. It seems wearied from the 

 labor of the spawning, and now takes no longer the same care of the last coming 

 eggs. 



The number of eggs deposited by one individual is very great, as is generally the 

 case amongst all the lower and unprotected animals. It will lay at repeated times a 

 day, and so during a week or two, as the eggs develope successively. It is even a 

 necessity for some to be expelled before the following ones can reach the oviduct and 

 complete their growth. ' 



There is but one yolk in each egg ; a single case was observed in which two yolks 

 existed, giving rise to two embryos, still in full life during the period of the motion, 

 when last observed. They were equal in size, and therefore one of them was not 

 separated from the other, as in fig. 14, unless the separation took place by equal parts. 

 Further on we shall witness a case in which, out of a unique sphere, two embryos is- 

 sued, though by an accidental process of the living fabric. 



