March 10, 1905.] 



SCIENCE. 



studying degeneration and the problems 

 connected with it. For the phenomena are 

 not exhibited here as isolated examples, but 

 as a continuous series in which every step 

 can be traced clearly. This, supplemented 

 by a study of the life histories of the dif- 

 ferent species, gives a first knowledge of 

 factors and conditions which aids greatly 

 in the drawing of rational conclusions. 



One of the problems is that which con- 

 cerns the cause, or rather the causes of de- 

 generation. Parasitism, while serving as 

 a stimulus or ultimate cause, can not oper- 

 ate directly in producing degenerative 

 changes. There must be other more im- 

 mediate causes which operate in connection 

 with it. 



These immediate causes have been studied 

 but very little; most writers are content 

 with the mere statement that the disuse of 

 a part or organ is what leads to its deterior- 

 ation and ultimate loss. But evidently 

 there must be some reason for the disuse, 

 and then if its effects are to be permanent, 

 and to go on accumulating until they re- 

 sult in the entire disappearance of the part, 

 they must be capable of inheritance. 



As a contribution towards the settlement 

 of this and other vexed questions a careful 

 study of the conditions and phenomena of 

 degeneration has been undertaken in con- 

 nection with the study of the morphology 

 and habits of these parasites. 



At present the study has extended over 

 the family Argulidce and the subfamily 

 Caliginje, with the following results : 



1. The Argulida3 show no signs of de- 

 generation ; there are many modifications 

 of organs in adaptation to new conditions, 

 but nothing that could be called a deterio- 

 ration. The reason for this is found in the 

 fact that they do not carry their eggs in 

 cases but deposit them lapon some con- 

 venient surface. An act so important to 

 the preservation of the species calls for a 



complete preservation of all the powers pos- 

 sessed by free-swimming forms. 



2. Of the Caliginte, some show as little 

 evidence of degeneration as the Argulid^, 

 while others furnish excellent examples 

 of it. 



The first step in this degeneration is a 

 loss of the lunule, or sucking disks, on the 

 frontal plates. Many causes contribute to 

 produce this effect. The bggs are carried 

 in cases and so retard locomotion ; they are 

 aerated by the movements of the host and 

 so do not require movement on the part of 

 the female ; the best food supply is situated 

 where there is the best aeration, so there 

 is no incentive to movement. 



3. The second step in degeneration is the 

 assumption of a fixed position ; here again 

 several causes may be found. The larvre 

 are attached to the host by a frontal fila- 

 ment and after maturing have no incentive 

 for moving about. On the disappearance 

 of the lunules the second antennge and sec- 

 ond maxillipeds are enlarged and their 

 claws serve for attachment organs. Claws 

 can not be attached and loosened readily, 

 but when once fastened securely there is a 

 tendency to retain the hold. 



The driving in of the claws makes a 

 wound and causes a flow of blood, the food 

 of the parasite ; it is easier to lacerate the 

 old wound than it is to make a new one; 

 and again the deeper the wound the more 

 plentiful the blood-supply. 



4. The third step in degeneration is the 

 modification of some part or organ in con- 

 sequence of the fixed position. For each 

 of these changes there are separate causes. 



Notes on the Development of the Gill in 

 Mytilus: Edward L. Rice, Ohio Wes- 

 leyan University. 



The early development of the gill of 

 BIytilus was worked out by Lacaze-Duthiers 

 in 1856. To his account of the develop- 

 ment of the earlier filaments the present 



