636 TRANSACTIONS OF SECTION D. 



in a norma] InacJms is the elaboration of a large quantity of yolk in the ovary 

 which fills about half the body. In an infected Inachus of either sex with 

 atrophied gonad this process of yolk-elaboration can be proved to occur since the 

 Sacculina roots manufacture yolk very similar to the ovarian yolk of a normal 

 female Inachus from the blood of the host. The parasite Sacculina, therefore, 

 forces the Inachus, whether male or female, to produce substances in the blood 

 from which it can manufacture yolk. As fast as these substances are produced 

 the Sacculina takes them up, and by anchoring them stimulates their continued 

 reproduction. These female yolk-forming substances, saturating the body fluids 

 of infected crabs both male and female, cause the development of the female 

 secondary sexual characters, and when the parasite dies and its roots no longer 

 assimilate the yolk-forming substances, they are taken up by the remains of the 

 gonad which consequently proceeds to form ova. In the case of Peltogaster on 

 Ihipagueus, Potts (Q.J. M.S., vol. 50, p. 599) has shown that small ova are formed 

 in the testes of the host while the parasite is still alive, so that here the excess 

 of the yolk-forming substances is taken up by the gonad during the life of the 

 parasite. This overproduction of a substance which is being anchored by a 

 parasite is closely analogous to the production of antibody in immunisation. The 

 crab doubtless benefits by supplying the Sacculina with the yolk-forming sub- 

 stance, as it thus protects other nutritional substances necessary for its vital 

 organs from being abstracted by the parasite. In this manner it is possible to 

 bring the isolated and hitherto inexplicable phenomenon of parasitic castration 

 into the well-known category of immunity. 



2. Coral Smiles and Peacocks. By Dr. H. F. Gadow, F.R.S. 



3. Relation oj Regeneration and Developmental. Processes. 

 By Dr. J. W. Jenkinson. 



Tn a broad sense ontogeny is distinguished from phylogeny ; in a narrow, as 

 the development of an organism from an egg-cell, from budding and regeneration. 



In development the three processes of cell and nuclear division, growth and 

 differentiation are easily recognised. Differentiation — the main problem — is deter- 

 mined by external factors, a definite constitution of the physical and chemical 

 environment being necessary, and internal. The latter arc : (1) The initial struc- 

 ture of the germ; (2) the interaction of developing parts. 



With regard to (1) Weismann's conception of the qualitative division of the 

 nucleus has been abandoned, for while we know (Boveri) that the chromatin 

 elements in the nucleus are unlike, we also know that each cell of the developing 

 organism must necessarily contain a complete specific set of these elements. 

 We turn then to the cytoplasm and find that experiments prove the existence of 

 definite organ-forming substances in it, arranged in a definite way, and some- 

 times stratified and graded. This arrangement accounts for the observed pro- 

 gressive restriction ot the potentialities of parts. Segmentation segregates these 

 substances into cells, but the order iii which the material is cut up is immaterial ; 

 the essence of segmentation is to reduce the ratio of cytoplasm to nucleus. In 

 regeneration — the production of a whole structure by a part in a differentiated 

 organism- similar processes and factors may be observed. 



Regeneration — of both internal and external members — is of practically 

 universal occurrence in the animal kingdom. The regenerate often differs quanti- 

 tatively or qualitatively (heteromorphosis) from the original. Reversal of polarity 

 is a special case of I he latter. 



Features common to all regenerations are the covering of the wound, the 

 cell-multiplication (to reduce the cytoplasm-nucleus ratio), growth — always at 

 right angles to the cut surface, and at a rate which alters like the ontogenetic rate 

 —and differentiation. Differentiation follows the ontogenetic order as a rule, 

 but may differ from it (anomalous behaviour of germ-layers). Of the external 

 factors little is known, but it is certain that the actual injury is the prime 

 stimulus. Internal factors are : Interaction of parts, size (there is a minimal 

 size), degree of differentiation (power of regeneration decreases with age), level 



