MUSEUM OF COMPARATIVE ZOOLOGY. 2G7 



newly forming organs in their relation to the cavity of the primitive 

 hydrophyllium. 



We recognize in this stage many organs which have already been de- 

 scribed, and one or two new ones lately formed. In the first place, the 

 yolk — a prominent spherical mass of polygonal segmentation spheres 

 with the internal protoplasmic network — should be mentioned. This oc- 

 cupies most of the middle portion of the figure. Around it in profile the 

 epiblastic and hypoblastic layers, of which the former is ciliated, may be 

 seen. The larger, more transparent body, seen above and on either side 

 of the yolk, is the projecting primitive hydrophyllium. This distal por- 

 tion of this scale is represented at the top of the figure, the proximal at 

 the lower part, while the right hand of the figure is the left of the scale, 

 following the nomenclature of previous descriptions. The nuclei of the 

 epiblast and the polygonal outlines of the epiblastic cells are easily seen 

 here and there over the surflice of the scale. The cavity {c.p. I.) of the 

 primitive larva has two or more thread-like structures {fd.) extending 

 from its hypoblastic lining to the nuclei of epiblastic cells. The hypo- 

 blast of the primitive cavity has a yellow color, especially well marked 

 at its distal end, where its walls are likewise covered with small pigment 

 dots, black, or nearly so, in color. At the opposite extremity of the 

 primitive cavity, near the float, it ends in a closed cone-like termination, 

 which is hidden by the float iu the figure. 



It is perhaps needless to say, that the spherical body near the middle 

 of the figure is the float, seen through the yolk contents ; and that on 

 the right and left sides of the primitive cavity are two buds, which later 

 develop into the serrated hydrophyllia characteristic of the Athorybia 

 stage. In both of these can be recognized a very thick outer layer, 

 which is probably the middle gelatinous layer, over which is spread a 

 thiu layer of epiblast, and an inngr thinner layer, which is hypoblast. 

 Within this last layer in each case we have a cavity which is the begin- 

 ning of the future tube which penetrates the scales. A considerable 

 quantity of reddish pigment is found in the yolk in the immediate neigh- 

 borhood of the last-mentioned orgiins. \X is very diflficult for me to 

 formulate any law for the relative position in which the successively 

 appearing buds of the larva of the Agalma develop. W^e know that in 

 the adult Affahna those nectocalyces which are nearest the float are the 

 youngest, and that the newly formed organs of this name always develop 

 between those already formed and the float. 



Fig. 2, PL IV. represents a very instructive stage in the development of 

 the primitive larva, which was taken on August 9 at noon, or on the third 



