2 LABORATORY DIRECTIONS 



Monotremata — egg-laying mammals: duckbill 



Marsupialia — pouched mammals: opossum, kangaroo 



Insectivora — moles, shrews 



Rodentia — rabbits, squirrels, rats 



Carnivora — cats, bears, foxes 



Chiroptera — bats 



Primates — monkeys, apes, man 



Ungulata — hoofed mammals: sheep, horse 



Proboscidea — elephant 



Cetacea — whales 



Amphioxus — A Primitive Chordate 



Although amphioxus is not a vertebrate, it is of great 

 importance in a study of comparative anatomy for it contains 

 vertebrate structures in a simplified condition and is by many 

 biologists thought to be similar to the ancestors of the verte- 

 brates. A knowledge of the anatomy of amphioxus will aid 

 greatly in understanding the origin of many vertebrate organs. 



Examine specimens of amphioxus that have been stained. 

 The pointed end is posterior. The head is poorly developed, 

 possibly degenerate. The expanded membrane at the anterior 

 end is the oral hood, which forms a cavity, the stomadaeum, 

 within. The mouth lies at the bottom of the cavity. The oral 

 hood is fringed with cirri or tentacles. A dorsal fin extends along 

 the back and continues around the posterior end as the caudal 

 fin. The two folds on the ventral side are the metapleural folds. 

 These will be mentioned again in connection with the evolution 

 of paired appendages. The metapleural folds meet at the atri- 

 opore, a depression on the ventral side serving as an outlet for 

 water used in respiration. The a7ius is near the posterior end 

 on the left side. The V-shaped muscle plates on the sides are 

 called myomeres. These are separated by sheets of connective 

 tissue known as myocommata (singular, myocomma). Along 

 either side may be seen the numerous gonads, segmentally 

 arranged. 



The internal structures can perhaps be studied best by 

 examining cleared mounted specimens and models and charts. 

 The mouth opens into the pharynx, a wide cavity extending 

 posteriorly into the straight intestine. The pharynx is per- 



