

X 



Dr. C. Chun on the Siphonophora. 161 



Muggicea. Although the investigation is attended with several 

 difficulties, arising from the minuteness and transparency 

 of the tiny ova, and, further, from the circumstance that we 

 can very seldom find at the same time male Eudoxice with 

 perfectly mature pin-shaped spermatozoa and female necto- 

 calyces which show themselves to he filled with fertilizable 

 ova by the characteristic pumping movements of the plasma 

 surrounding the nucleus, I have nevertheless, after several 

 vain attempts, finally succeeded in obtaining an artificial 

 fecundation, and furnishing the proof that from the ova of the 

 Eudoxia a ciliated embryo is produced, which grows into the 

 Monophyes. Seven mature ova which were contained in the 

 manubrium of a genital calyx, and one of which was just be- 

 ginning to issue from the ruptured ectodermal envelope, I 

 placed on the 23rd September in a vessel which swarmed 

 with spermatozoa taken from a male manubrium. As from 

 the scantiness of the material my special object was to rear 

 the later developmental stages, I forebore the observation of 

 the first phenomena of segmentation. In the warm season 

 they must take place rapidly ; for as early as the next 

 day I found to my delight seven free-swimming embryos. 

 The youngest represented a spherical planula, with thin 

 ciliated ectodermal cells and large polyhedrally flattened endo- 

 dermal cells occupying the whole interior space. It quickly 

 begins to assume an oval form, and at one pole differentiates 

 yellowish-red pigment. This represents the future buccal 

 pole, or, to speak more exactly, the spot at which the buccal 

 aperture of the stomachal polype breaks through. During 

 the rotating locomotion it is directed backward. At one side 

 of the pigmentless pole, which is in front as the animal ad- 

 vances, an ectodermal invagination is produced, the rudiment 

 of the subumbrella of the nectocalyx. Below this the body- 

 wall swells up in the form of a bud, from which, by various 

 repeated sinuations, the tentacle takes its origin. In the 

 meantime the endoderm divides, as already recognized by 

 Hackel and MetschnikofF, into a central cell-mass with dis- 

 tinctly perceptible nuclei, and a small cellular layer applied 

 to the ectoderm. The latter represents the definitive endo- 

 derm, while the former is gradually absorbed. The rudiment 

 of the nectocalyx enlarges considerably ; the vascular lamella, 

 with its lateral diverticulum, representing the future fluid- 

 receptacle, makes its appearance distinctly ; and the embryo 

 attains the form shown in fig. 6. On the third day (fig. 7) 

 the identity with Monophyes is unmistakable. The necto- 

 calyx is cap-shaped, shows distinctly the cavities of the four 

 radial vessels, with the annular canal, in its vascular lamella, 



