3 68 



NA TURE 



\_August 14, 1884 



the animal in which Chamisso discovered alternation of 

 generations, is not an example of alternation. 



The historical associations which render the life-history 

 of Salpa so interesting to the naturalist have induced me 

 to restate briefly my reasons for believing that the solitary 

 Salpa is a female and the chain Salpa a male ; since a 

 recent contributor to Nature (" Recent Morphological 

 Speculations," by R. N. G., in NATURE, May 15, p. 67) re- 

 jects my observations for reasons which a little examina- 

 tion will show to be inconclusive. 



The author characterises my opinion as " Brooks' 

 theory," but it is neither a theory, nor was I the first to 

 describe the phenomenon in question. Embryological 

 observations by Kowalevsky must be received by all 



Fig- I 



naturalists with the greatest respect, and I therefore call 

 the attention of R. N. G. to the fact that this great ob- 

 server published, while my first paper was in the press, the 

 following account of the life-history of Salpa (see Arch./. 

 Mik. Anat. \i. 604) : — " Bei den Salpen giebt es bekannt- 

 lich zwei Generationen, in der einen entwickelt sich der 

 aus vielen eikeimen bestehende Eierstock, welcher in den 

 Stul' 1 hineingeht, und sich hier zu je einem Eie vertheilt, 

 sodann die einzelnen Knospen resp. Kettensalpen in 

 welchen weiter aus diesem Eie ein Embryo entsteht, 

 wieder mit einem aus mehreren Eikeimen bestehende 

 Eierstock." 



No one will question the statement that the animal in 

 whose body an ovum is produced is the mother of the 



Fig. 2 



embryo to which this ovum gives rise, and if the egg which 

 is fertilised in the body of the chain Salpa is developed, as 

 Kowalevsky and I have stated, in the body of the solitary 

 Salpa, the latter is certainly a female, and as no one has 

 ever observed the production by a chain Salpa of more 

 than one embryo, either from an egg or by budding, there 

 is no true alternation of generations. 



This view is in no sense a " morphological speculation," 

 nor should it be spoken of as " Brooks' theory." It is 

 either an observed fact or an erroneous statement, and its 

 untruth can be proved only by observation. 



R. N. G. lays much stress upon the life-history of Pyro- 

 soma, a closely related but less modified form, and 

 regards it as an " indirect negation" of my statement that 



the solitary Salpa is a female, and the chain Salpa a male. 

 Our knowledge of Pyrosoma and of other Tunicates 

 certainly leads us to believe that Salpa is the descendant 

 of a hermaphrodite ancestor, but it proves nothing more. 



The fact that nearly all the Arthropods are bisexual 

 does not disprove the hermaphroditism of Balanus. It 

 simply shows that Balanus is the modified descendant of 

 bisexual ancestors. 



While the life-history of Pyrosoma cannot be quoted to 

 disprove the statement that the solitary Salpa has an 

 ovary, it can help us to understand the way in which the 

 present life-history of Salpa has been acquired, and thus 

 show that my own view is not very anomalous after all. 



As the phenomena are very complex, I have attempted 

 to exhibit the leading features by diagrams, and Fig. I 

 shows the points of greatest importance in the life-history 

 of Pyrosoma. 



The egg gives rise, by a process which does not here 

 concern us, to several sexual animals, one of which is 

 represented by A in Fig. 1. It has a testis, T, and an 

 ovary, O, which consists in part of " generative blastema," 

 and, in part, of ova in various stages of growth. It is, 

 therefore, a hermaphrodite. One of the ova, E, is very 

 much larger than any of the others. This hermaphrodite, 



A, produces a second, B, by budding, and during this 

 process part of the " generative blastema " from the ovary 

 of a passes into the body of b, and forms its ovary, o, 

 which here produces one fully developed ovum, E, and a 

 number of small ones. As B has a testis, T, it is a 

 hermaphrodite like A. 



The single mature ovum, E, of A, also passes into the 

 body of B, where it is fertilised and gives rise to an 

 embryo, EM, which undergoes development within, and 

 finally escapes from, the body of P., although A is its 

 mother, because the egg which has produced it was 

 formed in the ovary of A before the body of B was formed 

 by budding. 



B then gives rise by budding to C, and the single mature 

 egg of B passes into the body of C, where it is fertilised, 

 and gives rise to an embryo. 



Part of the "generative blastema" of b's ovary passes 

 into the body of the bud C, and becomes an ovary, O, 

 which again gives rise to one mature ovum, E ; and C 

 produces another bud, D, and discharges into it one ripe 

 ovum and part of the ovary in the same way, and so on 

 indefinitely. As c and D have testes like A and B, they 

 are all hermaphrodite. 



After the bud B has become independent of A, another 

 ovum is matured in A's ovary, another hermaphrodite bud 



