ZOOLOGY AND BOTANY, MI0RO80OPY, ETO. 973 



arms ; these curve upwards and inwards over the top. Below, the stem 

 terminates in a number of very slender, long, branching rootlets. With 

 the single exception of Chondrocladia clavata it is the smallest sponge known 

 to the author, its total length being only 24 mm., of which the stem 

 measures 11 mm. It was taken off the north-east of New Zealand, at a 

 depth of 700 fathoms, and, like other deep-sea Monaxonids, it has a definite 

 and symmetrical shape. The peculiar curvature of the pinnse suggests that 

 they may, during life, have the power of bending and unbending, but 

 unfortunately the condition of the specimen did not admit of any investiga- 

 tion into the presence of those contractile fibre-cells, which Prof. Sollas has 

 lately suggested should be called myocytes. Of the spicules, some of the 

 microsclera are peculiar for the possession of three elongated, fang-like 

 teeth at the small end of the spicule. 



Protozoa. 



Theory of Sexuality.* — M. E. Maupas sums up in a theory of sexuality 

 the results of his recent beautiful observations on the conjugation of ciliated 

 infusorians. It will be remembered that according to Maupas the micro- 

 nucleus is a hermaphrodite sexual element, of sole importance in conjuga- 

 tion. In the stage (A) it increases in size ; it then divides twice (B and 

 C), and eliminates the " corpuscles de rebut." This effected, it divides 

 again (D), differentiating a male and female pronucleus. In the next stage 

 (E) the male elements of the two conjugating Protozoa are exchanged, and 

 the new male nucleus fuses with the original female portion. In the next 

 two stages (F and G) the nuclear dualism characteristic of the Ciliata is 

 re-established (the old macronucleus having broken up and been eliminated 

 meanwhile). In the last stage (H) the ex-conjugates reassume their 

 original organization before dividing for the first time. 



What is the meaning of all this ? There is no special sexual reproduc- 

 tion or generation. There is no acceleration of division after conjugation. 

 It is a period of risk, especially during the inertia of reconstruction. 

 It is a loss of time. An Onychodromus grandis had from 40,000 to 50,000 

 descendants while a pair were indulging in a single conjugation. It is 

 a source of destruction, not of the multiplication of individuals. 



The riddle was solved by a long series of careful observations. In 

 November 1885 M. Maupas isolated a Stylonychia pustulata, and observed 

 its generations till March 1886. By that time there had been 215 fissi- 

 parous generations. But at that time the colony gave in ; the individuals 

 had lost the powers of nutrition and reproduction. Individuals removed 

 at various stages, however, had conjugated with members of different origin. 

 The same experiment was repeated with other forms. In March 1886 an 

 ex-conjugate from one of the couplings just referred to was removed and 

 watched till the 10th July, when the family again gave in. During that 

 time 315 divisions had been observed. Numerous conjugations had been 

 effected with members removed to other families. This was done till the 

 130th generation, and till then all the conjugations were fertile. About 

 the 180th generation individuals of the same family which had not 

 hitherto been in contact with one another began in despair to conjugate. 

 The results were, however, nil ; the conjugates did not even recover from 

 the effects of their forlorn hope. Other cases are related. 



The result is evident. The process is essential for the species. The 

 life runs in developmental cycles of multiplication by division, which are 

 strictly limited. If conjugations with unrelated forms do not then occur 



* Comptes Kendus, cv. (1887) pp. 356-9. 

 1887. 3 S 



