456 ZOOLOGY. 



careful search in tlie proper habitats, they have received considerable 

 attention within the last few years, and to Prof. A. A. W. Hubrecht, of 

 Leyden, we are indebted for an elaborate memoir on the group, published 

 in 1881. 



The most conspicuous feature of the group is " the presence of four 

 longitudinal nerve-trunks, united together into one in front of or above 

 the pharynx," and coalescing behind in whole or part (two of them) into 

 a ganglionic swelling above the rectum. 



In all the genera of the group "a heart, situated dorsally close to 

 the posterior extremity of the body, a median dorsal and a median ven- 

 tral blood-vessel, are the principal parts of the circulatory apparatus." 

 The respiratory apparatus is variable. In Chsetoderma and Neomenia 

 retractile brauchise are developed at the posterior extremity of the body, 

 in Chcetoderma being paired and in Neomenia being tuft-like; in Pro- 

 ueomenia special branchiae are absent, and respiration is supposed to 

 be effected through the wall of the intestine and the foot, "and per- 

 haps more especially in the rectum." 



There is a decided difference, it seems, in the relations of the sexes in 

 the two primary grouj)s of the class. The Chaetodermid£e, like the 

 Chitonids, have the sexes separate, while the Neomseniidae are monoe- 

 cious or hermaphrodite. There is a direct communication between 

 the ovary and pericardium (at least, in Chsetoderma and Proneomenia), 

 and the pericardium also communicates with the exterior by a system 

 of ducts and passages. Such ducts, in part, at least, are considered as 

 renal organs. "And so the Solenogastres exemplify a primitive stage, 

 in which the pericardium (body-cavity) receives the oviducts on the one 

 hand, and on the other communicates with the exterior by means of the 

 nephridia." 



It is maintained by Dr. Hubrecht that the deviations in this type are 

 rather manifestations of degradation or atrophy of parts than of incip- 

 iency and original non-development. The radula has been aborted or 

 lost, and not failed. The condition of the nervous system is expressive 

 of a reduction of type and is not a primitive stage, and the inferior 

 development of the intestine and liver is likewise to be looked upon as 

 a result of reduction. 



Americanised European Shells. 



Several species of well-known European sheUs have been introduced 

 into the waters of the Atlantic coast within recent years. A common 

 shell of England — Littorina littorea — was found on the shores of Maine 

 as early as 1868, and still earlier as an inhabitant of Nova Scotia. But 

 several closely related species were already known as common Ameri- 

 can forms. During the past year, however, two distinct family forms 

 have been added to the American Fauna — Truncatella trimcatula, the 

 type of the family of TruncatellidaB, and Assiminea grayana, also a type 

 of a peculiar family, the Assiminiidse. Both were found for the first time 

 by Professor VerriU among the docks of Newport, E. I., at high water. 



