444 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 



the eggs time to progress I discovered that they developed into normal 

 planulae and thus was forced to conclude that this strange and irregular 

 cleavage must after all be normal for the species. On several occasions 

 the attention of a number of other observers, who were working in the 

 same marine laboratory, was called to this phenomenon, and they also 

 expressed surprise and remarked that they had never seen segmentation 

 presenting such anomalous and irregular features. 



Metschnikoff describes and gives a few figures of a very similar 

 condition of segmentation in Oceania armata. He says: "Wenn bei 

 den beschriebenen Medusen verschiedene Abweichungen in clem 

 Zustandekommen des vierten Furchungsstadiums constatirt werden 

 mussten, so konnte man doch bei alien eine gewisse Regelmassigkeit 

 auffinden. Ganz abweichend in dieser Beziehung verhiilt sich 

 Oceania armata, da bei dieser Mecluse die kaum mit einander verein- 

 igten Blastomeren durchaus unregelmassig und ordnungslos neben 



einander liegen Das Abweichende in der Embryonalentwickelung 



der Oceania armata hort noch nicht so bald auf. Die Furchung 

 setzt sich in unregelimtssigster Weise fort und fiihrt zur Bildung 

 unformlicher Zellenhaufen, in deren Innern Mann eine Furchungshohle 

 durchschimmern sieht. Oft nehmen solche Embrvonen eine ganz 

 abenteurliche Gestalt an, deren Ursache zum Theil darin liegt, class 

 sie sich durch Theilung vermehren. Diesen Process habe ich an 

 mehreren isolirten Blastula-Stadien beobachtet, so dass ich an dessen 

 Existenz nicht zweifle." In Turritopsis, likewise, the later cleavages 

 take place in a most irregular manner and lead to the formation of a 

 shapeless and grotesque mass of blast omeres in which the cells are 

 frequently held together very loosely. The accompanying drawings 

 unfortunately represent only the most regular forms. This is due in 

 part to the fact that the very irregular forms were at first thought, as 

 stated before, to be abnormal; and partly because it was difficult to 

 make accurate camera sketches of these shapeless masses during life 

 while cleavages were taking place rather rapidly. 



Whether these embryos multiply by division, as Metschnikoff states 

 to be the case with Oceania armata and to which he attributes in part 

 the cause of their peculiar shapes, I have no direct evidence; but think 

 that it is very probable that such may be the case. Frequently the 

 blastomeres are separated into two distinct masses held together by a 

 small isthmus of cells. If they do not divide by an internal activity, 

 they must, occasionally at least, be broken apart by the action of the 



