SEISONID.E. 88 



to find, as both he and I have failed to find many similar spots, seen by Mr. Eckstein, on 

 the heads of various Eotifera. 



length, 7 \; to T V inch (Ehrenberg) ; ^ inch (P.H.G.) ; T ^ 7 inch (Eckstein). 

 Habitat. Watcombe (P.H.G.). 



Family SEISONID^, Plate (192). 



Elongate vermiform animals, Jg- to | inch in length, of similar form in both sexes ; 

 the males somewhat smaller, and less abundant, than the females. The body is divided 

 into four apparent segments, viz. the head, neck, middle body (trunk), and foot ; these, 

 with the exception of the last two, are sharply separated from each other. The neck 

 can be retracted in its whole length into the trunk, along its ventral surface. The 

 corona is rudimentary or wanting. The buccal funnel and oesophagus meet at the 

 anterior end of the mastax, which is thus a sacciform ventral appendage of the oeso- 

 phagus. In the head, two dorsal and two ventral, long-stalked, pyriform glands empty 

 their secretion before, or into, the mastax. Similar cells exist in the hind head ard 

 neck. Stomach elongated, formed of non-ciliated polygonal cells, and with two gastric 

 glands in front. Sexual organs paired, with a common dorsal evacuator ; that of the 

 male opening at the junction of neck and trunk ; that of the female, at the posterior 

 extremity of the trunk. Ovaries consisting of numerous distinctly separated ova. The 

 male sexual apparatus complicated ; having various parts, which may be regarded as 

 seminal vesicle, vas defere?is, and ductus ejaculatorius. Two lateral canals, furnished 

 with vibratile tags, traverse head, neck, and trunk ; and discharge themselves externally, 

 with the sexual organs. There is a dorsal nervous ganglion in the head, bearing 

 a dorsal antenna : there are no lateral antennae. The longitudinal muscles are strong, 

 the transverse feeble ; none are striated. The tail has a number of long-stalked, 

 pyriform, viscous glands, opening at the hind extremity of the foot. At the same point, 

 towards the ventral surface, there is a vesicle opening by a short, projecting canal, the 

 signification of which is doubtful. 



The animals are ectoparasites on Nebalia of the Mediterranean and North Sea ; 

 especially on their branchial laminae. Ephippial eggs do not occur. 



Genus SEISON, Grube (172). 



With an intestine discharging itself with the excretory organ ; so that the anal 

 aperture is situated differently in the two sexes. Coiona two tufts of cilia placed on 

 the anterior extremity. In the posterior half of the head 5-6 flask-shaped cells ; the 

 efferent duct of which passes into the fore part of the neck. Sexual organs of the 

 female placed ventrally to the stomach. The lateral canals do not fork in the trunk. 

 The ductus ejaculatorius of the male possesses well-developed muscles in its walls, and 

 performs undulatory movements. On the right side it forms a lobiform diverticulum ; 

 and opposite to this, on the left side, a multipartite glandular body. No spermato- 

 phores. The foot terminates posteriorly in an adhesive disc. The whole ventral 

 surface of the trunk is covered with a great number of transverse muscular fibres, and 

 thereby acquires a striated appearance. In the Adriatic near Trieste. 



SEISON GKUBEI, Glaus (17), (PL XXX, fig. 4). 



SP. CH. Trunk not annulated ; neck formed of three segments. See vol. ii. 

 p. 134. 



SEISON ANNULATUS, Glaus (18). 



SP. CH. Trunk divided into a large portion, and, following this, four short joints ; 

 the neck shows more than three rings. 



