320 



LOWER INVERTEBRATES. 



Fig. 393. — Haliotis, abalone. 



openings of the renal glands of both sides remaining, thus showing that the group is 

 more primitive than those which follow it. Another fact that also emphasizes this 

 inferiority is the absence of distinct genital ducts, the products of the reproductive 

 organs escaping by the larger renal opening. The lingual ribbon is well developed. 



The family Haliotid^ embraces the forms which are familiarly kuown as eai-- 

 shells, and to which the local terms ormer and abalone are applied in the Channel 

 Islands and southern California respectively. The shell is 

 spiral, the body whorl being flattened and very large. The 

 dorsal surface of the shell is perforated by a line of openings 

 through which pass a series of tentacular processes from the 

 ^'».a>Zrr'>sZ?+5-''l^ ^ mantle. As growth proceeds, these are closed up posteriorly. 

 The eyes are on short stalks. The forms are mostly tropical 

 and semi-tropical in their distribution, and are extensively 

 collected for their beautiful shells, which are an article of commerce. The shells 

 furnish a large proportion of the mother-of-pearl, especially that used in inlaying 

 papier macM ornaments. In France and the Channel Islands, ormers are used as an 

 article of food, but on account of their toughness they require pounding and mashing 

 before cooking. 



The FissuKELLiD^, or key-hole limpets, are structurally closely allied to the last 

 family, but in external appearance they seem far different. Tlie shell 

 is conical and shows but very slightly any spiral. The series of open- 

 ings of the Haliotis are replaced by a hole at or near the apex of the 

 shell, or by a notch in the front margin. On the inside of the shell 

 is a horseshoe-shaped impression, indicating the surface of attach- 

 ment of the muscles of the foot. The eyes, instead of being jslaced 

 on stalks, are scarcely elevated above the surrounding surface. Like 



the members of the last family, 

 the species are largely inhabi- 

 tants of the warmer seas of the 

 globe, although some forms are boreal in their 

 range. They are mostly found near the shores, 

 where they feed upon tlie smaller seaweeds. In 

 their habits they are not different from the other 

 limpets. 



The third family of the Zygobranchia, the 

 Patellid^, is apparently far different from 

 the other two in the structure of the gills, and 

 the fact that it really should have a place here 

 is shown by one of the neatest bits of morpho- 

 logical logic with which we are acquainted. On 

 the first examination of a Patella we find a res- 

 piratory organ in the form of a circle just be- 

 neath the mantle, while the branchiae above the 

 neck, comparable to those of Haliotis and Fis- 

 surella, are absent. Spengel, however, found 

 in this region two little prominences, the ho- 

 mologies and functions of which were obscure. The thought, however, suggested itseK 

 that these might be the rudiments of the true gills and an anatomical examination 



Fie. 394. — Fissur- 

 ella nodosa, key- 

 hole limpet. 



Fig. 395. — Under surface of Patella alqira ; 

 foot; 6, edge of mantle; c, gill; d, head 

 tentacles. 



