220 BULLETIN OF THE 



have studied and the youngest larva he figures. They diflfer from the stages 

 which he figures in the presence of the tentacle which always characterizes the 

 taster. A failure to raise one of these tasters separated from the colony into a 

 new colony, it might be said, does not prove that under other conditions better 

 results may have been reached. As a question of opinion, it is regarded as 

 highly doubtful that the colony of Nanomia reproduces by budding, and that 

 the new colony is ever formed from a taster. Nanomia, however, us shown by 

 Agassiz, has an egg development, and passes directly from a planula-like young 

 into stages similar to the youngest which he figures. It is therefore thought 

 that the embryo, without exception, is derived from an egg. The segmenta- 

 tion of the egg was observed, and, as nothing has ever been published on the 

 egg of Nanomia, a few stages in the segmentation are here represented. 



The egg of Nanomia, like that of Agalma and other genera, is transparent, 

 colorless, almost invisible in the water. The interior is penetrated by and 

 almost wholly made up of a spongy mass of protoplasm, forming a network 

 filling the contents of the egg. A thin covering of protoplasm surrounds the 

 egg. Metschnikoff * describes in the egg of Epibulia a similar network, and 

 the author! has devoted some space to a consideration of the same in Agalma. 



The first change (Plate II. Figs. 1, 2) in the external contour of the Nano- 

 mia egg is the formation of a primary cleavage-furrow. This furrow was formed 

 by the bending in of the outer wall of the egg at one pole. This infolding of 

 the primary furrow leads to well-marked folds on the outer wall of the egg, 

 which recall the phenomenon of " Faltenkranz " in some other animals. In 

 about an hour's time after the first appearance of the infolding to form the 

 primary furrow, a 2-celled cleavage stage was formed, and the first cleavage 

 plane (1 cZ) is well developed. About another hour elapses before the sec- 

 ond cleavage plane is formed and a well marked 4-cell stage (Figs. 4, 5) is 

 developed. 



In his paper on the development of Agalma the author points out the pecu- 

 liar warping of the first cleavage plane by the formation of the second. It 

 was there shown, that by the growth of the second cleavage furrow at right 

 angles to the first, it was brought about that the plane of the first cleavage 

 was broken near the equator of the egg. In the same way "and by an analogous 

 process in the development of the Nanomia egg the second cleavage plane is 

 60 formed that the continuity of the first plane is likewise broken. Figure 4 of 

 Plate II. illustrates this broken condition of the plane in Nanomia. Whether 

 this modification is of any morphological importance, or has any influence in 

 subsequent development of the cells, cannot be at present determined. The 

 8-cell stage is produced by the formation of two new furrows (Fig. 6) bending 

 in on one side of those cells already formed in a way analogous to that already 

 described in Agalma. 



* Studien iiber die Entwickelung der Medusen und Siphonophoren. Zeit. f. 

 Wiss. Zo6\., Bd. XXIV. 



t On the Development of Agalma, Bull. Mas. Comp. Zool., Vol. XI. No. 11. 



