CEPHALOCHORDA. 349 



The tentacles are smooth and without any sensory patches. 



The preoral pit is large, and in structure is similar to that of A. lanceolatus. The blood 

 vessel running with it breaks up into a glomerulus, in which the vessels are less in number 

 but of a larger sectional area than usually obtains in the European species. In this point 

 there is some variation, certain of the specimens approaching more nearly to the former type, 

 others more to the ty^e as described by Andrews. 



The " Raderorgan " is large and well formed. It consists of a large dorsi-lateral arm on 

 each side of the buccal hood, and thin secondary arms with smaller loops in between. The 

 dorsal arm of the left side is longer than that of the right, and connects up with the pz'eoral 

 pit. The whole organ forms a ring of tissue round the base of the buccal hood, the arms 

 being pulled out along its sides. 



The mouth and velum underlie the apex of the eleventh myotome. There are eight velar 

 tentacles. The pharynx stretches between the level of the apices of the 10th to the 45th 

 myotome, thus occupying a space a little over half the total length of the body. Both mouth 

 and pharynx as well as the alimentary canal are similar in structure to the corresponding 

 organs in A . lanceolatus. The skeletal bars of the gills are normal in general plan, but the 

 synapticulae joining the bars together are only three in number and very slender. 



The nervous system presents no great peculiarities, the most noticeable feature being the 

 absence of the olfactory pit, no traces of which could be found. The nerve cord stretches 

 to the tip of the caudal extremity as a very fine thread. Special nerves are given off 

 only in the region of the myotomes. Beyond this point, i.e. in the caudal extremity, no 

 nerves arise from the nerve cord. 



The excretory system consists solely of patches of epithelium on the floor of the atrial 

 cavity. No trace of nephridia on the gills could be seen, nor could Lankester's brown funnels 

 be traced. Andrews was similarly unable to find these in the Bahama form, so that their 

 non-existence seems certain. 



The circulatory system (of which only the main vessels were traced) is similar to that 

 of A. lanceolatus. 



The gonads are placed on the right epipleur, and are twenty-nine in number, lying from 

 the 14th or 15th to the 43rd or 44th myotomes. The first few gonads are small. They 

 present a gradual increase in size till the centre of the series is reached, after which they 

 again begin to decrease, the last few gonads being of the same size as the first. The period 

 of sexual maturity seems to bear no relation to the size of the animal. Very small specimens 

 were found with well developed gonads (always 29 in number), while some of the largest 

 obtained, measuring 30 mm., had them very little or not at all developed. 



2. HETEROPLEURON MALDIVENSE. PI. XVIII. fig. 2. 



This species is by no means common in the Maldive Islands, only four specimens being 

 obtained from Mahlosmadulu Atoll. None were found in the lagoon of the Island of Minikoi, 

 and since Mr Gardiner searched this locality extremely carefully during the months of June, 

 July, August and September without finding either adults or larvae, it may be concluded that 

 it does not occur there. 



45—2 



