1895- RESULTS OF '^ CHALLENGER'' EXPEDITION. 69 



branchial and atrial apertures. A little group of three species, for 

 which the new genus Edeinascidia has been founded, forms a con- 

 necting link between the previously known Clavellinidae and the 

 Ascidiidae, and shows that the group of Social Ascidians, established in 

 1828 by Milne Edwards, must now be merged in the Ascidiae Simplices. 



The geographical distribution of the Simple Ascidians is very 

 wide ; but it appears from the " Challenger" investigations that they 

 are not specially abundant in the northern hemisphere, and are com- 

 paratively scarce in tropical latitudes, while they attain their greatest 

 numerical development in southern temperate regions. The bathy- 

 metrical range is also wide, extending from the littoral zone down to 

 2,900 fathoms ; still they are mainly a shallow-water group, and are 

 found in greatest abundance immediately around the coast in a few 

 fathoms of water. 



Altogether the " Challenger " collection of Tunicata contained 

 184 new species (in addition to a number of marked varieties), and 

 these have required the formation of twenty-one new genera, and 

 three new families — the Ccelocormidae, the Polystyelidae, and the 

 Octacnemidae. Among the theoretical conclusions that have been 

 deduced from their study are : — • 



1. That the Tunicata are to be regarded as a degenerate offshoot 

 from the Protochordata, with some primitive Clavellinid as the 

 ancestral form of the fixed Ascidians. 



2. That Pyrosoma, although now a pelagic free-swimming or- 

 ganism, was derived from the fixed Compound Ascidians. 



3. That Ascidiae Compositae are an unnatural or polyphyletic 

 group, having probably been derived from the ancestral Simple 

 Ascidians at three distinct points — the result being that the Compound 

 Ascidians form three groups: (i) the Polystyelidae; (2) the Botryl- 

 lidae ; and (3) the remainder, which are more nearly related to par- 

 ticular groups of Simple Ascidians than they are to one another. 



W. A. Herdman. 

 Vertebrata. 



Fishes. — The great contribution to Ichthyology made by the 

 "Challenger" Expedition, was the provision of a broad and sure 

 foundation of our knowledge of the abyssal fish-fauna. In the intro- 

 duction to his volume on the " Deep-sea Fishes," Dr. Albert Giinther 

 has already clearly stated the extent of this contribution and sum- 

 marised previous knowledge of the subject, so that it is unnecessary 

 to do more than quote from his observations. Risso, in 1826, was the 

 first to distinguish an abyssal fish-fauna, and he not only assigned to 

 it certain species, but also attempted to state the depths at which 

 they habitually Hve. Between 1843 and i860 the Rev. R. F. Lowe's 

 researches among the fishes of the ocean round Madeira added the 

 further important fact that some fishes live during their earliest stages 

 at or near the surface, while they retire into comparatively great 

 depths in the course of their growth. He also determined the precise 



