234 DISCOVERY REPORTS 



In Doloria the nucleus of the nauplius eye nerves consist of three equal ovoid 

 glomerular masses associated with three equal small nerves. In Gigantocypris the nucleus 

 consists of two large glomerular masses, one on either side of the median plane. This 

 is what might be expected from the structure of the eye in which the lateral components 

 are enormous compared with the median and also from the fact that the small nerve 

 from the median portion always joins with one or other of the much larger lateral nerves. 



From the nucleus of the nauplius eye two giant fibres run back to the level of the 

 protocerebral bridge. In Gigantocypris the brain is very much compressed antero- 

 posteriorly so that the latter structure lies close against the more posterior central body. 

 In this region the giant fibres appear to bifurcate and extend laterally. The left branches 

 of each join and extend outwards to the nucleus of the paired eye of the left side. The 

 right branches behave in a corresponding manner. This nucleus appears as a simple 

 spherical glomerular mass close against the sides of the protocerebral bridge. It does 

 not show the distinctions into lamina and medulla as in Doloria, neither is there a large 

 connective mass of nerve fibres between it and the central body. 



The nauplius eye is thus linked directly by a chiasmatic giant fibre system to the 

 nuclei of the paired eye. This is important as the paired eyes are certainly not the 

 usual type of ocular organ. They may even be described as rudimentary. In more 

 typical Cypridinids the paired eyes are normal and function normally, and the optic 

 centres are connected through the system of tracts associated with the central body with 

 the other important centres of the nervous system. In Gigantocypris, although the 

 paired eyes have ceased to function in the normal manner and the predominant organ 

 is now the nauplius eye, the latter has continued to use the association or distribution 

 centre of the paired eyes for the co-ordination of its activities. 



The most important point about the internal anatomy of the nervous system is that, 

 apart from the giant fibres I have just described, there appear to be no others in the 

 whole system. The significance of this is that it throws further light on the meaning of 

 a giant fibre system generally. 



In a recent paper on the functioning of the giant fibres of the squid, Young (1938a) 

 has pointed out that the mantle has a double nerve supply — a system of relatively small 

 fibres which are presumably used in the ordinary movement of respiration and a giant 

 fibre system to be used for rapid movement. In another paper (19386) he has drawn 

 attention to the fact that the Octopod Cephalopods having developed the use of their 

 arms for walking have given up the more rapid contractions of the mantle such as occur 

 in the squid and at the same time have lost their giant fibre system. This all fits in with 

 the views expressed by Miss Lowe (1935) in her monograph on the anatomy of Calanus. 

 In this paper she describes the giant fibre system and shows that in addition to acting 

 as a co-ordinating system within the central nervous system it supplies all and only 

 those muscles which are used in the escape reaction, previously analysed cinemato- 

 graphically by Storch (1929). 



Now in Doloria I showed that the giant fibres outside the central nervous system only 

 supply the massive muscles of the second antennae and it is these muscles that are used 



