INDUSTRIAL PROGRESS DURING THE YEAR 1875. clxxxv 



From his study of the curious worm Sagitta M. Giard 

 supports the prevalent view that it is a worm standing near- 

 er the annelids than any other animals. In his essay he 

 notes the characters these animals share with others leading 

 a pelagic life, which are as follows : 



1. An extreme transparency of all the tissues, which ren- 

 ders the animal completely invisible, and enables it to es- 

 cape easily from its enemies. We observe it in the JYbcti- 

 lucce, the Siphonophora, the 3fedusce, the Ctenophora, the 

 Heteropod and Pteropod mollusks, the Salpce and Pyroso- 

 mata ; in Sagitta, Tomopteris, and Alciope, and, lastly, in 

 the Leptocephali, among fishes. 



2. The unusual development of certain organs of sense, es- 

 pecially the eyes, and sometimes the auditory apparatus, as 

 in the Medusse and the Appendicularia, and in My sis. 



3. The small size of the digestive tube. 



4. A considerable development of the organs of genera- 

 tion, and great fecundity. 



5. A great number of pelagic animals present the phenom- 

 ena of phosphorescence, such as the JVbctihtcce, many 3Iedusa?, 

 the JPyrosomata, and Phyllirhoe bucephala. This phosphor- 

 escence, which is manifested especially when the animals are 

 excited or alarmed, no doubt acts as a protection, and stoj^s 

 the pursuit of some enemies. 



6. Their social life, as many of them swim in large masses. 

 M. Villot has made some observations on the migrations 



and transformations of certain marine parasitic Trematodes. 

 Two very different Distomoe live in the intestine of the sea- 

 lark, a kind of plover. One is Distoma leptosomum, and the 

 other D. brachysomwn. These two parasites are found in 

 the larval state, still encysted, in the gizzard of the sea-lark ; 

 in the small intestine they are further developed, and when 

 they arrive in the rectum they have acquired their adult 

 size, and laid their eggs, which are ready to be expelled. As 

 to the tadpole -like young (cercarise) of these Distomas, 

 those of D. brachysomum become encysted in small isopod 

 crustaceans of the genus Anthuva ; while those of D. lepto- 

 somum are encysted in a small mollusk Serobicularia te- 

 nuis. The crustacean and mollusk both serve as food for the 

 sea-lark. Professor J. Leidy notices some parasitic worms 

 in the Proceedings of the Academy of Natural Sciences at 



