The Genus Synchceta. By C. F. Eousselet. 405 



L. H. Plate from material collected by Dr. 0. Nordqvist in the 

 Bay of Bothnia. The specimens having been killed and preserved 

 in spirit, were all fully contracted, so that only a very imperfect 

 description could be given. Dr. Levander has, however, found this 

 form again in great abundance in the open sea near Helsingfors, 

 and has given a better account of it with a drawing. He has 

 also been good enough to send me some fairly well preserved 

 specimens and two sketches of the dorsal side and front view of 

 the head, which are here reproduced (figs. 12 and 12a), so that I 

 owe my acquaintance with this peculiar Synchaeta to these. Not 

 having seen it in the living state, however, my account of it must 

 be largely taken from Dr. Levander's description. 



The shape of the body is quite unlike that of any other 

 Synchfeta, and instead of the usual cone it presents an extremely 

 thin-walled, very transparent, bag-like, rounded vesicle, constricted 

 anteriorly, with a very small head, which, however, has the usual 

 characteristic Synchseta structure. The body terminates in a very 

 small swollen foot carrying a single toe. 



The whole structure of all the organs is so fine and delicate 

 that it appears evident the whole organism, in acquiring these 

 characters, has been evolved with a view to render itself as trans- 

 parent, and therefore as invisible as possible, which is characteristic 

 of many pelagic animals. 



The small head, as will be seen from fig. -12a, which represents 

 a front view, carries a normal ciliary wreath in two interrupted 

 regions, four frontal styles, and two small but distinct auricles. 



The cervical eye is red, seated on the oval brain mass. The 

 dorsal antenna is slightly raised above the eye, while the ventral 

 antennas emerge very low down close to the foot, somewhat on the 

 ventral side. The mouth is shield -shaped and guarded by the 

 usual screen of fine hairs. The mastax is also small, of Synchseta 

 structure, and the unci have five strong teeth, which I was able to 

 see in some swollen specimens where the unci had been forced 

 through the mouth. 



The oesophagus is a very thin, long tube, not ciliated internally, 

 leading to a small thick-walled stomach, to which very small and 

 rounded gastric glands are attached. 



The ovary is very small, oval, containing about eight germ- 

 cells. 



The muscular system is of normal character ; a dorsal and 

 ventral pair of extremely thin and narrow muscular threads 

 originate both in the head and in the foot, and are inserted a little 

 below the middle to the body-walls. 



The excretory system is represented by lateral canals, which 

 are attached, on either side, to the wall of the stomach, whence 

 they continue forward for a short distance, being suspended quite 

 freely in the body-cavity by a very fine thread attached to the side 



