56 PROCEEDINGS OF THE AMERICAN ACADEMY 



was before a single body or sac becoming two, which are attached in 

 a monibform manner. The new germs thus formed may consist each 

 of a single cell only, as I have often seen ; but they soon attain a 

 more uniform size by the endogenous formation of new cells within 

 the sac in which it is inclosed. In this way the germs are multiplied 

 to a considerable number, the nutritive material for their growth 

 being apparently a fatty liquid, in which they are bathed, contained 

 in the abdomen, and which is thence derived from the abdomen 

 of the first parent. When these germs have reached the size of 

 about one three-hundredth of an inch in diameter, there appears 

 on each, near the inner pole, a yellowish, vitellus-looking mass 

 or spot, composed of yellowish cells, which, in size and general 

 aspect, are different from those constituting the germ proper. This 

 yellow mass increases after this \)eviod, pari passu with the germ, and 

 at last lies like a cloud over and partially concealing one of its poles. 

 I would, moreover, insist upon the point, that it does not gradually ex- 

 tend itself over the whole germ-mass, and is, therefore, quite unlike 

 a proligerous disc. 



" When these egg-like germs have attained the size of a one- 

 hundred-and-fiftieth of an inch in diameter, there begins to appear 

 distinctly the sketching or marking out of the future embryo. This 

 sketching consists at first of delicately marked retreatings of the cells 

 here and there ; but these last soon become more prominent from 

 sulcations, and at last the form of an articulated embryo is quite 

 prominent. 



" During this time, the yellowish, vitellus-looking mass has not 

 changed its place, and, although it is somewhat increased in size, yet 

 it appears otherwise the same. When the development has proceeded 

 a little further, and the embryo has assumed a pretty definite form, 

 the arches of the segments, which have hitherto remained gapingly 

 open, appear to close together on the dorsal surface, thereby inclosing 

 the vitellus-looking mass within the abdominal cavity. It is this same 

 vitelloid mass thus inclosed, which furnishes the development of the 

 new germs (which in this case would be those of the fourth colony, 

 or D), and this germ development here commences with the closing 

 up of the abdominal cavity, and then the same processes we have just 

 described are repeated. 



" The details of the development subsequent to this time, the for- 

 mation of the different systems of organs, &c., are precisely like 



