192 C, F. ROUSSELET ON TEOCHOSPH/ERA SOLSTITIALIS. 



to declare that the side on which both the mouth and cloaca 

 open is really the dorsal side of the animal. But then the usual 

 dorsal gap in the ciliary wreath and single dorsal antenna, which 

 are both very distinct, would in this animal be situated on the 

 ventral side. I think, however, there is a better way out of the 

 difficulty, and that the cloaca is only apparently ventral when in 

 reality it is dorsal. By comparing T. solstitialis with a few other 

 rotifers the true relation of this organ will be shown. Asplanchna 

 p'iodonta has no intestine, but it has an uro-genital cloaca, 

 which also opens apparently on the ventral side of the animal. 

 Asplanchnopus myrmeleo is like Asplanchna in this respect, and 

 has in addition a foot protruding on the ventral side ; the uro- 

 genital cloaca also appears to open on the ventral side, but 

 closely behind and dorsal to the foot. Notojys hyptopus has a 

 ventrally situated foot and an ano-uro-genital cloaca again 

 situated apparently on the ventral side, but dorsal to the foot, 

 which is generally admitted to be the dividing line between the 

 dorsal and ventral side of a rotifer. It will be seen, therefore, 

 that in the rotifers having no foot there is no clear indication as 

 to where the dorsal side begins ; and I think the best explanation 

 in the case of Trochosphmra solstitialis will be to say that the 

 ventral side ends just before the cloaca, and to call the whole 

 tract, from the gap in the trochal wreath to the cloacal orifice, 

 dorsal. In this way the cloaca and all other organs will appear 

 in the usual position which obtains throughout the class. 



The flat ribbon-like ovary is suspended between the body wall 

 and the stomach, and opens by a thin-walled oviduct in the 

 cloaca. The lateral canals are attached on each side close to the 

 walls of the sphere, and appear to open in a small contractile 

 vesicle ; their apparent connection with the nerve threads of the 

 lateral antennae does not appear to me to be real or organic, 

 but only accidental. Two red eyes, with crystalline lenses, are 

 present, situated on the ciliary wreath in a line at right angles 

 to the mouth. The nervous system is very distinct, and can be 

 beautifully studied in this animal ; the brain gangHon is seen just 

 above the mastax, sending long and short nerve-threads across 

 the body cavity to the dorsal and lateral antennae, to the ciliary 

 wreath, the eyes, and all other organs. Two long and two 

 short gastric glands attached at the apex of the stomach, and 

 four or five pairs of small muscular bands arranged just below 



