358 Copepoda living as Messmates with Ascidians. [Sess. 



0. F. Miiller. It is sometimes buried so deeply in the 

 substance of the test as to be almost entirely concealed, 

 and where it can only communicate with the outside world 

 by means of a small passage having an opening on the outer 

 surface. Dr J. Gwyn Jeffreys, referring to this mollusc, 

 remarks that sometimes a score of specimens may be extracted 

 from a single large Ascidian. I have also found in cells 

 formed in the tests of Ascidians several specimens of the 

 curious little Amphipod, Tritceta gihhosa ; while zoophytes of 

 several kinds have been seen adhering to various other parts 

 of its surface. 



But if, having finished the examination of the outside of the 

 test, we proceed to investigate the inside of it, perhaps the first 

 of the objects to be observed will be one or two specimens of 

 Zeucothoe spinicarpa Abildgaard — a moderately large, soft- 

 bodied, and sluggish Amphipod of a pale flesh colour, and 

 bearing green-coloured ova. Then there are nearly always 

 present in the branchial chamber a number of Copepoda which 

 may belong to several distinct species, and thus it sometimes 

 happens that the capture of a large Ascidian may turn out to 

 be a miniature treasure-house to the marine zoologist. 



The Copepod-messmates of Ascidians have had a good deal 

 of attention devoted to them, especially by Continental zool- 

 ogists, and the results of recent study seem to favour the 

 opinion that in development and structure they exhibit a . 

 more or less near relationship with Cyclo^ys. But this rela- 

 tionship, though obvious in some cases, is obscure in others. 

 There are, for example, a few species that resemble Cyclops 

 somewhat closely, both in their general appearance and habits. 

 Like Cyclops, they carry two external ovisacs ; they are active 

 in their movements, gliding freely and quickly over the walls 

 of the branchial chamber. These forms belong to the Licho- 

 molgidse, and their affinity with Cyclops is so evident that they 

 have been classified along with that group and some other 

 Copepoda in the division Cyclopoida. It may be observed in 

 passing that while there are Lichomolgi which pass their lives 

 as the messmates of these Ascidians, there are other species 

 belonging to the same genus that live a free life amid the 

 forests of Laminaria and zoophytes which in some places 

 fringe our shores, and it has been suggested that the forms 



