REPORT ON THE CRUSTACEA MACRURA. fl"23 



Sylon hippohjtes, M. Sars, is 10 mm. in length and 7 in breadth; Sylon sehneideri 

 had a very different size in the specimens I was able to investigate ; in one the dimensions 

 were about 3'1 by 2'1 mm., in another the length and the greatest breadth measured 

 6 and 4 - l mm. respectively. I have also seen a specimen of Hippolyte pusiola with two 

 small specimens of Sylon sehneideri attached to it ; the one about 1 - 5, and the other 

 2 mm. in length. 



The specimen of Sylon challenger*' which was sent me was not quite uninjured. As 

 is shown in figs. 1 and 3, PI. CXLIX., the outer wall of the body was torn open in front, 

 aud this damage, caused perhaps by the desire of the artist to see as much as possible of 

 the animal without detaching it from the Spirontocaris, at first caused some difficulty 

 in the determination of the animal. In Sylon the outer surface of the body is quite 

 .smooth and bears no appendages or trace of segmentation ; the large and very distinct 

 opening found in the other JRhizocephala, which Delage calls the cloaca, is wanting in 

 this genus. For the communication of the mantle-cavity with the exterior two rather 

 small round holes alone are present, which were accurately observed and figured by 

 M. Sars. From analogy I am of opinion that they were situated just within the limits 

 of the damaged part of the body of Sylon challengeri ; and a comparison with the figure 

 of Sylon sehneideri attached to Hippolyte pusiola (PI. CXLIX. figs. 4, 5) will readily 

 convince any one of the probability of this supposition. In fig. 5 a lateral view is given, 

 and in fig. 4 a front view ; in both figures the circular openings exist at a., and they are 

 about 0"3 mm. in diameter. In young specimens these openings seem to-be closed ; at 

 all events I observed them in this condition in a small specimen of Sylon sehneideri, a 

 transverse section of which is represented on PL CL. fig. 2. Like other Ehizocephala, 

 Sylon carries its developing ova within the mantle-cavity ; Krbyer's observations on the 

 larvas of this genus, and his comparison of these larvae with those of Sacculina, admitting, 

 I think, of no doubt on this point. Most probably the Nauplii, when ripe, leave the 

 cavity by means of the above-mentioned openings. Punning from between the two 

 openings towards the place of attachment, a narrow stripe is visible through the trans- 

 parent outer wall on both sides, limited by a distinct clear line (PL CXLIX. fig. 4). 

 Here the body of the Sylon seems to be attached to the interior of the mantle, and pro- 

 bably this stripe is comparable to the •" mesentere " of Delage. 



When I commenced my investigations I did not know the nature of the parasite, and 

 I therefore decided upon studying it by means of transverse sections. I was obliged to 

 detach it from its rather bulky host, taking away along with the parasite an annular part 

 of the body of the Shrimp. Fig. 2, PL CXLIX. was made after the animal had been 

 thus loosened, and represents it from below. The round smooth part (e) afterwards 

 proved to be the very dense mass of ovarian tubes. The outer covering was so loosely con- 

 nected with the interior, that I was obliged before embedding it in paraffin to take it 

 quite away; and in so doing I neglected to investigate microscopically the mode in which 



