NOTES ON THE ANATOMY OP DINOPHILUS. 43 



fig. 13). The further relations of the body-cavity may be con- 

 veniently considered in connection with the excretory and repro- 

 ductive systems. 



Nephridia. — Like D. gyrociliatus, as figured by Ed. Meyer (11, and 

 as described, on Meyer's authority, in Lang's Polycladen, p. 678), 

 D. tseniatus possesses five pairs of nephridia, whose arrangement is 

 in some respects different from that of the same organs in B. gyro- 

 ciliatus. It may be at once noted that the occurrence, in two species 

 so distinct as B. gyrociliatus and B. tseniatus, of five pairs of 

 nephridia, raises the question whether the body may not possibly 

 consist of five metameres throughout the genus Binophilus, in spite 

 of variations in the number of the ciliated rings. Thus, according 

 to Korschelt (6), RepiachofE (12)* and Meyer (11), B. gyrociliatus is 

 characterised by the possession of seven post-oral ciliated rings (one 

 of which is perianal), in spite of which fact there only five pairs of 

 nephridia. It may, however, be noted that Korschelt figures (pi. 

 xxii, fig. 43) a recently hatched (female) individual, in which the 

 body consists of six segments, sharply marked off from one another, 

 in addition to the tail. 



In the female D. tseniatus the five pairs of nephridia are all alike, 

 whilst in the male the fifth pair is modified as a part of the genera- 

 tive apparatus. The fifth nephridia of the female occur in the fifth 

 segment of the body, on the ventral side of the intestine (behind the 

 caecal end of the stomach). The fourth nephridium has exactly the 

 same position with regard to the stomach as the fourth nephridium 

 of the male ; it lies behind the posterior ovarian lobe. The third 

 nephridium is situated between the two lobes of the ovary, whilst the 

 second and first nephridia are in the same position as in the male sex. 



The following, more detailed description refers entirely to the male, 

 in which the nephridia can be more easily investigated than in the 

 female. The general arrangement of the system may be understood 

 from fig. 15, which illustrates the anatomy of a male B. tseniatus as 

 seen from the ventral surface under a compressorium. The figure of 

 course represents the combined results of a long series of observa- 

 tions, but it must be premised that the opacity of the animal was 

 sufficient to prevent any complete elucidation of the structure of the 

 nephridia. 



The first four pairs of nephridia may be considered together. 

 Each nephi-idium opens to the exterior on the ventral side of the 

 body, and probably not far from the longitudinal nerve-cords. The 

 observation of the exact point where the nephridium pierces the skin 



* Eepiacboff is strongly of opinion that there is no specific difference between Korschelf s 

 2). apairis and the earlier described D. gyrociliatus- 



