217 



Simple unpaired gonad, without 

 genital ducts. 



Sexes separate. 



Ova or eggs are small, and are shed 

 into body cavity. 



Larva (known as Ammocoetes) has 

 an endostyle functional as such ; 

 and the mode of feeding is like 

 that of Amphioxus. There is no 

 sub-pharyngeal tube distinct from 

 the pharynx. 



Freshwater and marine species. 



As in Lamprey. 



Ova are large (in horny cases with 

 adhesive threads), and are shed 

 into body cavity. 



Marine. 



What is Palaeospondylus ? 



A small extinct creature, found as a fossil in the Old Red 

 Sandstone. It is possibly a " lamprey " ; probably " a 

 Dipnoan, either larval or an adult form of small size and 

 primitive structure." 



DIVISION GNATHOSTOMATA. 



SUB-DIVISION ANAMNIA. 



CLASS PISCES (FISHES). 



State the general Characters of Fishes. 



Fishes are aquatic vertebrates which breathe by gills 

 chiefly, and which have unpaired and paired fins with 

 skeletal supports ; the paired pectoral and pelvic fins being 

 blade-like non-digitate fore- and hind-limbs.* 



The skeleton consists of cartilage, supplemented or largely 

 replaced by bone.* The notochord is generally replaced 

 by a segmented vertebral column. The skull and visceral 

 arches are well developed ; the first or mandibular arch 

 forms the upper and lower jaws,* which bear teeth. The 

 skin generally bears scales,* which are either partly dermal 

 and partly epidermal (placoid scales or skin teeth of Elasmo- 

 branchs), or wholly dermal (thin bony scales of Teleosteans 

 and thick bony plates of Ganoids). The skin has also 

 glandular cells and sensory structures (e.g., ampullae of 

 head region, lateral lines along the body). The brain is 



