On Asplanchna Ebhesbornii. By Dr. Hudson. 625 



on each side, whicli are attached to the dorsal surface near its 

 hinder extremity. 



TJie Nervous System. — There is a nervous ganghon of a rect- 

 angular shape, just under the surface of the trochal disk, touching 

 the mouth on its dorsal side and carrying the crimson eye. From 

 its four corners spring nervous threads ; two of these pass to the 

 setigerous antennae on the trochal disk, and two to similar 

 antennae, one on each side of the dorsal surface. One of these 

 latter is well seen in fig. 3, and its magnified rocket-like extremity 

 is shown at fig. 8. The trochal disk has however four setigerous 

 antennae, one at the top of each of its cones, and one on the inner 

 side of each towards the mouth. The four are nearly in a hue, and 

 the nervous thread on each side of the body swells out into a kind 

 of ganglion, when underneath the antennae, and sends ofi" a branch 

 to supply each. 



Leydig has drawn nervous threads from each of the four 

 antennae of the trochal disk, but figures them as passing separately 

 to the main ganglion. Of course this may be the case in A. Sieholdii, 

 which he was describing ; but in A. Ehheshornii there is only one 

 principal nerve-thread on each side of the body passing to the 

 antennae, and it supphes the two antennae on the same side by 

 branching just under the inner one. So much I think can be 

 distinctly made out ; but such a network of muscles and fibres 

 crosses the trochal disk, and so restless is the animal when held 

 down for observation, that I strove in vain to make out any further 

 details with certainty. 



Bejproductive System. — The female has a horseshoe-shaped 

 ovary ; of a cylindrical shape in the middle, but flattened out at the 

 ends, so as to remind one of the merrythought of a chicken. It is 

 hung by fine muscular threads between the stomach and contractile 

 vesicle, which latter it appears to clasp round. The germs of the 

 future ova are seen imbedded in its slightly granular substance, and 

 appear to consist of several cells each. The ova appear always to 

 be developed at the arched end of the ovary ; and, when they have 

 attained some size, they drop off" into the ovisac, which is a funnel- 

 sbaped pocket, with its broad base attached to the hinder end of the 

 contractile vesicle. The ovisac ends in an oviduct, which opens on 

 the ventral surface by a rather long transverse slit. This apparatus 

 can be best seen by dark-field illumination, as its walls are of 

 extreme delicacy. Occasionally I have met with specimens that had 

 as many as three or four ephippial eggs in the ovisac at once ; but 

 generally there is only one matming ovum (fig. 17), or a young 

 animal that has already left the egg, and lies across the parent with 

 its head presented to the opening of the oviduct. The bii-th of the 

 young is almost instantaneous, but the force used to expel so large 

 a foetus is sometimes fatal to the young ; for I have seen it issue 



