ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 471 



seems to be nearest Darwin's B. terebratus,\)\xi is perhaps a link between 

 Balanus and other genera {Acnsfa and Fijrgoma) ; Acasta Idrsuta sp. n., 

 fixed to a Plexaurid colony ; and A. anti^jathidis sp. n., on an Auti- 

 patharian. 



Crustaceans of Colombia.* — A. S. Pearse reports on a collection he 

 made about Santa Marta, on the southern shore of the Caribbean Sea. 

 He discusses the varied habitats — sea, mangrove swamps, streams, forest, 

 and desert. Fiddler-crabs {Uca) and Sesarmas were very common 

 among the mangrove roots. The rapid mountain streams contained the 

 amphibious crabs of the genus Pseudotelphusa, and the Isopod Fhiloscia 

 nitida. When the streams lose the impetus of their descent they are 

 invaded by hordes of shrimps and prawns. Swamps supported an 

 abundance of Entomostraca and a few fresh-water crabs. The rain- 

 forest showed a large number of Isopods. Some of the streams of the 

 desert along the coast had characteristic Crustacean inhabitants, and 

 Ccmobita diogenes wandered about among the sparse vegetation in rocky 

 situations. 



Many Crustaceans, like Amphibians, are in process of transition 

 from aquatic to terrestrial life. Every gradation is shown — marine, 

 fresh-water, terrestrial, arboreal. The variety is facilitated by the habit 

 of carrying the eggs about, the omnivorous habits, the protective 

 cuticle, and the plasticity of behaviour in relation to special conditions. 

 Eespiration appears to be the chief factor which has kept the majority 

 of Crustaceans in aquatic habitats. In their migrations there have 

 been three main highways : (1) Through the rivers to the land ; 

 (2) from ocean directly to land ; and (3) from marshes to swamp 

 habitats in fresh-water. The seclusive habits of Crustaceans have 

 doubtless been a great help to them in their landward migration. 



Annulata. 



Study of Cirratulus.f— F. W. Flattely has studied Cirratidus 

 {Audouinia) tentaculatus, a littoral Polychaet with elongate rosy or 

 yellow branchial filaments. It shows marked " thigmotactism," em- 

 bedding its body so that there is pressure on it from stones. The 

 filaments have no prehensile function, as has been asserted. They are 

 extremely elastic and lengthen out as the worm burrows. Some may 

 stretch for three inches up to the surface of the sand or mud. The 

 heart-body is strongly developed, and may secondarily act as a valve, 

 preventing regurgitation and keeping the filaments turgid. The animal 

 feeds on Algal spores, fragments of decaying Alga3, diatoms and organic 

 debris, which are selected outside the body. Two sensitive ciHated 

 flaps in the mouth are closely apposed when the mouth sucks in food, 

 and prohibit the entrance of any but the smallest food particles. These 

 are wafted backwards by the cilia of the gut epithelium. The filaments 

 certainly do not catch food particles or collect sand particles. 



* Proc. U.S. Nat. Museum, xlix. (1915) pp. 531-56 (4 pis.). 

 t Journ. Mar. Biol. Assoc, xi. (1916) pp. 60-70 (7 figs.). 



2 K 2 



