1^2 



ZOOLOGICAL SOCIETY BLTLLETIN. 



test or cell, but usually the whole of the test is 

 calcified, with the exception of the aperture 

 through which the tentacles are extruded. In 

 the largest group {Chilostomes) , the aperture is 

 guarded by a membranous, hinged operculum 

 which is shut down like a trap door when the 

 animal is retracted. In another group {Ctenos- 

 tomes), a circle of bristles guards the aperture. 



For the protection of the colony, a majority 

 of the Chilostouies have developed peculiar or- 

 gans known as avicularia and vibracula. These 

 structures are really highly modified individuals 

 which have undergone great changes, both func- 

 tionally and structurally, and have lost by degen- 

 eration all the internal organs except the muscles 

 of the operculum, which are greatly hypertro- 

 phied. In tlie case of the avicularium the oper- 

 culiun has become modified into a beak-like or- 

 gan, and in the vibraeulum the process is carried 

 still farther so that the beak becomes a long 

 lash-like organ. These organs are kept in 

 motion snapping or lashing back and forth to 

 prevent other forms from taking up their abode 

 on the surface of the colony. There is good 

 evidence to show the evolution of the avicular- 

 ium from the ordinary individual. The struct- 

 ure obtained its name from the fact that in 

 certain genera {Bugiila, Bicellaria) it is shaped 

 like the head of a bird and mounted on a neck- 

 like stalk. This is a highly modified condition, 

 however, and the simplest type is found sessile 

 between other cells of the colony and scarcely 

 distinguishable from them except in the size of 

 the beak. Spines and protuberances are also 

 of frequent occurrence in the Bri/ozoa and aid 

 in protection. 



The presence of sexual reproduction has al- 

 ready been mentioned. The eggs are developed 

 in the spacious body cavity and in some forms 

 are retained there until ready to be liberated as 

 free-swimming larvae. In other cases a special 

 brood-sac or ovicell is formed to harbor the em- 

 bryos until ready to be released. There are two 

 quite distinct types of ovicell, according to their 

 manner of formation. In the group of Cyclos- 

 tomes one or more individuals of the colony be- 

 come especially modified to serve as a brood- 

 chamber for the colony. In the Chilostomes, on 

 the other hand, a special organ may be formed 

 by each fertile individual. The eggs migrate into 

 this ijouch and undergo their later development 

 there. The ovicells are very characteristic of 

 the different species, and when present they 

 offer one of the best means of identification. 

 The develojiment of brood-chambers serving the 

 same physiological purpose but of different 

 origin affords a splendid example of the power 



of functional adaptation in bringing about 

 parallel evolution. 



The number of species of these interesting 

 animals to be found in the immediate vicinity of 

 New York City has not been determined. More 

 than eighty species have been taken by the 

 writer within a short distance of Woods Hole, 

 Mass. Probablv the number about New York 

 City is considerably less than this, as most of 

 the species require purer sea water than our 

 harbor affords. Several species have been suc- 

 cessfully kept in the Aquarium and some of 

 these liave attracted considerable attention when 

 exhibited enlarged a few diameters in the lens- 

 exhibit aquaria. R. C. O. 



THE FRESHWATER EEL. 



THE breeding habits of the eel, until very re- 

 cent years, have always been a mystery to 

 the naturalist as well as the angler. The 

 ancients believed that eels were generated spon- 

 taneously from the mud, while among fishermen 

 the notion is still prevalent, in some places, that 

 eels are the males of catfish. Such superstitions 

 as the above arose naturally in the attempt to 

 explain the absence of eels with spawn in streams 

 or ponds where the species may abound — and 

 of course mud and catfish are abundant every- 

 where ; and although naturalists have known 

 that tlie eels nnist breed normalh' like other 

 fishes, yet how, when and where? 



The first step toward clearing up these ques- 

 tions was made by Dr. Theodore Gill's sugges- 

 tion nearly fifty years ago (ISG-t), that the 

 ribbon-like, pelagic fish known as the Leptoce- 

 phalus is the larva of the Conger eel. This was 

 later proved to be true (1885), when Delage 

 succeeded in rearing the Conger eel tlirough its 

 metamorphosis from the Leptoccphahis. 



The metamorphosis of the common European 

 eel, {Angxtilla vulgaris), was discovered in 1897, 

 by two Italian zoologists, who proved that the 

 larva known as Leptocephalus hrevirostris de- 

 velops into the elver or young eel of this species. 

 This study was made in the Straits of Messina 

 at the point where Charybdis. the fabulous 

 daughter of Poseidon, was supposed by the an- 

 cients to draw ships to their destruction in the 

 depths of a whirlpool. In the currents at this 

 point many abyssal animals are brought to the 

 surface, and among these were obtained the 

 lepfocephali of the European eel. 



Extensive studies carried on in recent years 

 by Dr. Joh. Schmidt for the Danish government 

 have brought to light the following remarkable 

 facts: (1), the fresh water eel must return to the 



