426 M. Leuckart on the genus Sacculina. 



Arcmea, on which, as far as I know, it has not yet been observed. 

 It was of moderate size, 6 lines long and the same in breadth; 

 in its form it differed so much from the ordinary Sacculina 

 that I think I am justified in describing it .as a distinct species 

 [Sacculina inflata, n. sp.). The dorsal and ventral surfaces 

 were considerably arched ; and the posterior orifice, which is ex- 

 traordinarily extensible, was situated upon one of the surfaces 

 at some distance from the margin of the body (PI. VII. fig. 5). 



Although, by the anatomical examination of this single spe- 

 cimen, I by no means obtained even an approximately complete 

 insight into the structure of this animal, some remarks upon it 

 may not be out of place here, considering the complete uncer- 

 tainty of our present knowledge. 



In the first place, I have scarcely any doubt that the so-called 

 sucking-pit of our animal is actually the mouth. This view is 

 especially supported by the fact that this so-called sucking-pit 

 does not, as would be supposed from the previous descriptions, 

 merely adhere to the body of the Crab externally, but, with its 

 funnel-shaped margins, completely penetrates the integuments in 

 the membranous interstices between two segments, so that the 

 tolerably wide and gaping orifice surrounded by these margins 

 stands in direct communication with the % cavity of the body of 

 its host. No mandibuliform structures or projections could, 

 however, be detected on these margins. That the fluids of the 

 cavity of the body of the Crab pass into the interior of our Sac- 

 culina is, under these circumstances, a matter of course*. Close 

 behind the oral funnel, as also in the posterior extremity of the 

 body of this parasite, a broad and clear space (that is to say, a 

 space filled with colourless fluid) was seen shining through the 

 integuments, which can hardly be anything but the intestinal 

 canal filled with the blood of the Crab. This space attained its 

 greatest development at the hinder extremity of the body, where 

 it extends above the middle on the dorsal surface (the surface 

 turned from the posterior orifice). It is true that after the 

 opening of the Sacculina, when the fluid just mentioned flowed 

 out, no structure could be found, amongst the confusion of the 

 masses floating in the interior, that could be recognized with 

 certainty as an intestine, or even as a reservoir of the above 

 fluid ; but if we consider that even in Lerncea, the wall of the 



* According to recent observations by Wright and Anderson (Edinb. 

 New Phil. Journal, vii. p. 312), a canal rises from this oral orifice in Pelto- 

 (jaster Paguri, which, after entering the body of the host, becomes much 

 ramified, and penetrates this in every direction. [Thompson says, " On 

 removing them (the parasites) by force, the neck presents the appearance 

 of irregular branched joints, and a large opening is seen, which has every 

 appearance of being continuous between the rectum of the Crab and the 

 cavity of the parasite," — W. S. D.] 



