TRANSACTIONS OF SFOTTON P. 635 



more, into the tissue of the lobe. From a very early stage in the life of the 

 worm the form of these chaetse changes but little, except in regard to size, 

 which increases, of course, with the growth of the worm. Tt is evident that 

 during life new chaetse must be constantly in course of formation to replace 

 the older ones which are cast off, and the peculiarity of form and complexity of 

 arrangement suggested that special provisions might be expected. By means of 

 serial sections but little information could be obtained, but on rendering the 

 lobes transparent it was found that, running lengthwise in each lobe, there exist 

 two 'nests' for the formation of the chaetae, the outer one supplying 'the outer 

 paleae, and the inner one supplying the middle and innermost pal ess, which are 

 packed alternately in the 'nest.' The paleae develop in the 'nest.' commencing 

 as minute hooked or angular particles, and chaetae in an advanced stage can 

 be clearly seen travelling through the tissue in a somewhat spiral fashion in 

 order to reach in rotation the positions which they respectively take up at 

 the dorsal end of each opercular crescent. The foregoing remarks refer to 

 Sabellaria alveolata, and apply equally to Sabellaria spinulosa; but in the latter 

 species I have discovered in each lobe two or three long curved acicular 

 dorsal chaetae in addition to the three rows of chaetae which form the operculum. 

 In certain members of the family (Pallasia) the operculum is armed with two 

 rows of chaetae only, but there exist in addition two or more hooks, placed 

 dorsally, in position corresponding with the acicula above mentioned. These hooks 

 have been considered by some zoologists homologous with the missing middle row 

 of opercular chaet'ae, but in view of the existence of the dorsal chaetae of Sabellaria 

 spimdosa, in addition to the complete three rows of opercular chaetae, such a view 

 scarcely seems tenable. 



The above are, of course, only notes on an episode in the formation of the 

 operculum, to the minuter details of which T hope to give further attention. 



TUESDAY, SEPTEMBER 6. 

 The following Papers were read : — 



1. Sex and Immunity. By Geoffrey Smith, M.A. 



One of the principal effects which a parasite may exert on its host is to confer 

 immunity upon it. Immunity to a poison or poisonous organism is due to the 

 presence in the blood or body fluids of a substance or substances which combine in 

 some manner with the poisonous substances and prevent them reaching the tissues 

 in an active form. Ehrlich has given a graphic representation of this process in his 

 side-chain theory, according to which an organic poison when it enters the body 

 anchors itself to certain side-chains of the protoplasmic molecules, and these being 

 unable to take up nourishment are regenerated in excess and cast off into the blood 

 stream, where they act as antibody by seizing on the poison and preventing it 

 reaching the tissues. 



Besides the well-known phenomenon of immunity a peculiar effect of parasites 

 on their hosts, especially among the invertebrata, is found in the Castration, 

 Parasitaire of Giard. It has been found that the presence of certain parasites 

 causes the atrophy and sometimes the disappearance of the gonads of the host, 

 together with peculiar changes in the secondary sexual characters. A careful 

 analysis of a particular instance (the parasite Sacculina on the spider crab 

 Inachvs) has shown that the real effect of the parasite is to cause the male host 

 to assume adult female characters externally and after the death of the parasite 

 internally ;is well, large ova being produced from the testes; and in the case of 

 the female host the effect is really the same, as the young infected females are 

 forced to assume adult female characters at a premature stage. (See Q.J.M.S., 

 vol. 54, p. 577, and vol. 55, p. 225.) The object of this paper is to suggest that 

 this peculiar reaction to the presence of a parasite is really an immunity 

 phenomenon. 



We have seen that the effect of Sacculina on Inachvs is to make the latter 

 become adult female in character. Now the most important adult female character 



