254 BULLETIN OF THE 



formation of the first cleavage, when we have an 8-cell stage. From 

 this we pass into morula stages, in which additional cleavage planes 

 were not successfully traced as they originate, and in which the primary 

 and secondary planes could not be recognized as such. 



Before leaving the stage (fig. 7) in which the egg was found at 3 h. 

 45 m. p. M,, let me mention an appearance in the egg which was not un- 

 derstood, but which may have a significance in the embryology of these 

 animals. At the point in the egg adjacent to the break which has taken 

 place in the direction of the primary furrow, a depression is formed 

 winch resembles an opening leading into the interior of the ovum. 

 From the arrangement of the cell walls in the immediate vicinity, it 

 seemed as if this opening was formed by the drawing apart of the walls 

 of the cells, but whether it is the result of decay or not cannot be at 

 present stated. The single egg in which it was observed, however, 

 afterwards died before passing into advanced larval conditions. 



It is at about this time in the development of the Ac/alma egg that 

 some of the most extraoi'dinary examples of protoplasmic elevation from 

 its surface were observed. The resulting changes in external form often 

 baffle all attempts to observe accurately the normal outlines of the cells 

 of the segmented egg. These rhizopodal prominences are most clearly 

 marked in those eggs which have been in long captivity, and seem 

 wdiolly different in different ova. 



Before closing our account of the segmentation, let us compare our 

 observations with those of other naturalists on the same or closely allied 

 genera. Tlic poverty of our knowledge of the segmentation of the egg of 

 the genus Agahna is so great, that I find few descriptions in the writings 

 of others available for comparisons. MetschnikofF, although not figur- 

 ing the segmentation of the egg, evidently observed it, as the following 

 mention indicates. He says,* " Die Dotter zerkliiftung, resp. Larven- 

 bildung findet auf dieselbe Weisc statt, wie ich oben fiir EpihiiUa au- 

 rantiaca angcdcutet habe und wie sic bei alien von mir heobachteten 

 Siphonophoren als Eegel gilt. Was aber die Vorgange der Organbild- 

 ung betrifFt," he continues, "so finde ich die meiste Analogic mit den 

 von Haeckel nntersuchten Cri/sfallodes rigidimi und Atlioryhia rosacea, 

 obwohl auch in dieser Beziehung Agalma Sarsii manches Eigenthiim- 

 liche darbietet." Turning for further information to his account of the 

 segmentation in Einhulia we find him devoting a few significant para- 

 graphs to this interesting process. He says,t " Die bald auf das freie 

 Ablegen (esgelang mir nie kiinstlich aus dcm Schlauche bcfreitc Eier 

 * Op. cit., p. 49. t Op. cit., pp. 40, 41. 



