144 THE FAUNA OF THE DEEP SEA 



send special branches to a number of small papilli- 

 form processes on its outer surface. This system 

 of highly vascular processes probably constitutes, as 

 Professor Herdman suggests, an additional or com- 

 plementary respiratory apparatus. All these modifi- 

 cations of the branchial system are of particular 

 interest, for we find so many instances of a similar 

 kind among the inhabitants of very deep water. 

 I need only refer here to the modifications of this 

 system in the Isopod Bathynomus already referred 

 to (p. 129), and to the reduction in the number of 

 the gills of many of the deep-sea fishes. Why there 

 should be such modifications is a question upon which 

 the physical and natural history investigations of the 

 conditions of life in the great depths of the ocean at 

 present throw no light. 



In a previous chapter 1 have referred to the fact 

 that many of the bathybial animals are character- 

 ised by being stalked. Among the simple Ascidia we 

 find many examples of stalked kinds living in deep 

 water, such as Culeolus and Fungulus, but also several 

 exceptions, such as Baihyoncus^ Styela hythiij and 

 Ahyssascidia, that are sessile. It is a noteworthy fact, 

 however, that the genus that has the most deep-sea 

 species — namely, Culeolus — is a genus that is provided 



