4H2 STTMMAKY OF CUKIiENT ISESEAIICUKS REI.ATINO TO 



muscular system was found to bo very well developed ; tliat of the 

 hooks was very complicated ; the suckers arc princii)ally innervated 

 by branches from the principal lateral and from tlio secondary gan- 

 glia. T. eWtptlcn exhibits some dilTereuces from T. coenurus in tho 

 arrangement of the muscles. 



Tristoma molce, Hirudo medicinalis, and Myzostoma glabrum are next 

 successively discussed; the subjects among tlic Mollusca were P<ero- 

 trnchica coronnta, Pncumodermon meditcrruneum, Arr/onauta argo, and 

 Scpiola rondeJetii ; Ecleneis remora, Lcpadogaster gouannii, and tlio 

 counnon tadpole complete the series. From this wide survey it 

 results that suckers have very different forms in different animals; 

 simplest in tadpoles, they become powerful and wonderful organs of 

 fixation in the Cephalopoda. As, however, we have to deal with 

 analogues and not with homologues, we cannot draw any conclusions 

 as to the relationships of the animals examined. The fact that, 

 among the Echinodermata, we cannot find points of structure distiu- 

 guisliing the several orders, shows that the suckers are all adapted 

 from a common type ; there are here common characters, though not 

 always the same function. The Tasniida^ have suckers which differ 

 in structure from those of the BothrioceiDhalidaj ; and the distinctions 

 are such as to lead us to suppose that these organs had not the same 

 origin. On the other hand, tho sucker of Hirudo has much in 

 common with the abdominal sucker of the Tristomida ; this resem- 

 blance does not, in the judgment of the author, justify us in sup- 

 posing that these two groups have had a common origin ; all that it 

 shows is that there has been an adaptation of tissues to a function, 

 which has been everywhere subjected to the same mechanical condi- 

 tions. 



The Mollusca exhibit three distinct types which are seen in the 

 Pteropoda, Heteropoda, and Cephalopoda ; there is a great analogy in 

 structure between those of the first two, but the Cephalopoda differ 

 very markedly from them. " Thus the comparison of the organs of 

 suction of tho Cephalopoda and Pteropoda does not permit us to 

 advance anything which can speak in favour of the relationship 

 which it has been desired to establish between these two orders." 

 The hooks appear to be derived from the suckers in the Cephalopoda ; 

 this question is discussed at some length. 



The dorsal disk of Echeneis differs from the ventral disk of the 

 Discoboli in origin, morphology, and mechanism. 



Suckers are grouped into four sets : 



1. Suckers without a skeleton (Cestoda, Tristomida, Discophora, 

 Pteropoda, Heteropoda, Amphibia). 



2. Suckers with an internal calcareous skeleton (Echinodermata). 



3. Suckers with a horny external skeleton (Cephalopoda). 



4. Suckers with an osseous skeleton (Fishes). 



New Coelenterates and Echinoderms.* — Prof. A. E. Verrill de- 

 scribes new marine forms obtained by the S.S. ' Albatross ' in 1884 from 

 the outer banks off the southern coast of New England. The most 



* Am( r. Journ. Sci., xxix. (188.5) pp. 149-57. 



