i8o 



HA RD WICKE 'S SCIENCE- G OSS J P. 



or tunnel through rocks, or they cluster in the curls 

 of the snaky seaweeds, or they embellish coral caves, or 

 they lie scattered broadcast in countless myriads over 

 the chequered floor of the ocean. They occur of all 

 sizes from the dimensions of a hempseed to that of a 

 man's head, from barely a line to over two feet in 

 length, from barely a grain to four or five pounds in 

 weight. Their forms are of infinite variety (some 

 20,000 recent species are known), their beauty is 

 eminent, and they are endowed with a few anatomical 

 structures, physiological features, and native instincts 

 which suffice to place them in an exalted position 

 among the invertebrata. In addition to the more 



n;^ 



Fig. 123.— Principal nervous centres in Doris, a a, cerebroid ; 

 6 /', branchial ; c c, pedal — all communicating with one 

 another by slit5. 



Fig. 124— Upper poitlon of digestive organs of Eolis (after 

 Hancock and Ambleton). a, buccal mass ; b, cesophagus : 

 d, bulb of stomach ;/, intestine ; g, great central canal, which 

 ramifies into the papilhe ; /;, branches of great central canal ; 

 /■, ducts from glands of papillae. 



general qualities of excitement, irritation, a desire of 

 escape from danger, and a facility in sharing particular 

 food, some species of this tribe exhibit a perception 

 of time and of locality, and a capability of sociality 

 and of concerted action. Many fight lustily for the 

 protection of their ova, and construct a nest for them ; 

 some of the cuttle-fishes have been observed to make 

 love right " spoonily,"' to exhibit rivalry, jealousy, 

 and irascibility ; and even to display attachment to 

 their keepers, a jealous hate of intruders at aquariums, 

 &c. Briefly we may recount that the Mollusca possess 

 a distinct excito-motor and sympathetic nervous 

 system with very scattered nervous centres, which 

 control excito-motor, and probably sensori-motor 



movements ; also they have five senses ; muscular 

 tissue (which frequently exhibits the transverse stripes 

 of the voluntary muscle of the vertebrates) ; alimentary 

 organs ; an auriculo-ventricular (sometimes a portal) 

 heart, with attached veins, sinuses, and arteries with 

 colourless or pale blue corpusculated blood, and 

 breathing organs to aerate it ; they propagate by 

 eggs, and generally the young undergo one larval 

 stage of development. 



Fig. 125. — Teeth from palates of Doris, i, D. tjiberculaia ; 

 2, D. Joluisto^ti; 3, D. pilosai 4,/?. bilamellata (X loo). 

 All magnified. 



Fig. 126. — Diagram illustrating the difference between the Gill 

 of Doris and the Papilla of Eolis. A. Gill of Doris ; a, affe- 

 rent blood-vessel ; e, efferent blood-vessel ; b, enclosed spongy 



. tissue. B. Papilla of Eolis ; c, gland lined with granular 

 matter, loose or enclosed in large globules ; (f, oval chamber 

 filled with bags of thread-cells ; /, two narrow ducts whereby 

 the thread-cells can be discharged externally ; ^, muscular 

 tissue with blood-vessels. 



To range over the entire field of investigation 

 presented by these organisms, would in the space at 

 our command be impossible. We propose, therefore, 

 to offer a few remarks relative to the natural history 

 of a group of Mollusca which are, perhaps, less 

 popularly known than the other groups thereof, and 

 which indeed require a special search in order to 

 discover their whereabouts, or even their very^ 



