110 M. L. Plate on Ectoparasitic Rotatoria 



jecting canal, the signification of wliicli is doubtful. The 

 animals live ectoparasitically upon the species of NehaJia of 

 the Mediterranean and North Sea, especially on their bran- 

 chial laminae. They creep about after the fashion of geome- 

 tric caterpillars, and deposit their ova in groups. At the 

 commencement of development one or two polar corpuscles 

 appear ; all its stages are passed in the %gg. Special per- 

 sistent (winter) eggs do not occur. 



Genus I. Seison, Grube. 



With an mtestinej which discharges itself with the excre- 

 tory organ, and therefore places the anal aperture in different 

 parts of the body in the two sexes. Kotatory apparatus rudi- 

 mentary, formed by two tufts of cilia placed at the foremost 

 pole of the body. 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. The sexual organs of the female are 

 placed ventrally to the stomach. The aquiferous vessels do 

 not fork in the trunk. The ductus ejaculatorius of the male 

 possesses a well-developed musculature in its walls, and per- 

 forms undulatory movements. On the right side it forms a 

 lobiform diverticulum, and opposite to this on the left side a 

 multipartite glandular body. No spermatophores. The tail 

 terminates posteriorly in an adhesive disc. The whole ven- 

 tral 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. 



1. Seison Grubii, Glaus, — Trunk not annulatedj neck 

 formed of three segments. 



2. Seison annidatus, Glaus. — Trunk divided into a large 

 portion, and, following this, four short joints; the neck shows 

 more than three rings. 



Genus II. Paeaseison, gen. nov. 



In both sexes without intestine. Rotatory apparatus either 

 as in Seison, or reduced to a few tactile setas, or entirely 

 wanting. In the hind-head only two flask-shaped glands, 

 which open into the oesophagus in the commencement of the 

 neck. Sexual organs in male and female placed laterally or 

 dorsally to the stomach, only exceptionally displaced below 

 it. Each aquiferous vessel with five flicker-organs, and giving 

 off a thin-walled, csecally terminating lateral branch in the 

 anterior part of the trunk. The ductus ejaculatorius of the 

 male with smooth walls, with no movements or lateral organs, 

 with numerous flask-shaped spermatophores. The tail does 



