Turner, Nervous System of Cypris. 37 



As to the function of this organ, I have no definite proof; 

 but I am inclined to think that it functions as an eye. In 

 Cypridinay besides the usual compound eye. Dr. Claus has 

 described a median, unpaired simple eye. Now I am inclined to 

 think that this pear-shaped organ of Cypris is homologous with 

 the unpaired simple eye of Cypridina. At first blush, there 

 are two facts that seem to militate against such an assumption 

 1st, the median eye described by Claus is unpaired, while this 

 pear-shaped organ is distinctly paired ; 2nd, the median eye 

 described by Dr. Claus is near to the compound eye, while this 

 pear-shaped organ is far removed from the compound eye. In 

 spite of these opposing facts, there are several weighty consid- 

 erations which lead me to hold to the statements made above. 

 1st, Cypridina is much less compact than Cypris; 2nd, in 

 Cypridina the compound eye and the simple eye are situated 

 near the centre of the shell ; 3rd, in Cypridina the parts of the 

 compound eye are widely separated, while in Cypris they are 

 closely approximated. May it not be that in the ancestors of 

 Cypris the compound and simple eyes lie near each other and 

 near the middle of the shell, as it now is in Cypridijia f May it 

 not be that when the compound eye migrated towards the 

 dorsal surface, the simple eye migrated towards the ventral ? 

 And when' we remember that in histology this pear-shaped 

 organ resembles the invertebrate simple eye, we have, I think, 

 sufficient grounds for calling this a simple eye. To be sure this 

 pear-shaped organ is one of a pair while the simple eye of 

 Cypridina is unpaired ; but in this day, the phenomena of 

 transformations due to fission and to fusion are too well known for 

 this difference to merit even a passing consideration. The set- 

 tlement of this question, however, must be left to embryology. 

 Sense Organs of the Mouth. — In this same region of the 

 body, there is another set of hitherto undescribed sense organs. 

 From the caudal border of the upper lip, from the cephaHc 

 border of the lower lip, and from between the teeth of the 

 mandible, arise numerous hairs [fig. 16]. These hairs are some- 

 times plumose [fig. 35]. At the base of each of these sets 

 of hairs there is a similar sense organ [fig. 16, B, C, D\ Each 



