ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 209 



to take but little part in the process. Dismemberment appears to occur 

 regularly at the close of the breeding season, when the posterior region 

 of the body is thrown off. This is rapidly regenerated ; and the process 

 is probably explained by the fact that, in this posterior region, the 

 organs — save the gonads — undergo degeneration during the development 

 of the elements. The ordinary fission on irritation the author regards 

 as protective. He is not of opinion that the posterior region cau regrow 

 a head, but its death occurs slowly, and the sexual products may ripen 

 in it before death ensues. 



Ova and sperms were obtained freely from specimens kept in con- 

 finement, and the process of fertilisation observed. The polar bodies do 

 not appear till after fertilisation, and display that form of protoplasmic 

 activity described by Andrews as " filose activities or spinning." The 

 egg also displays spinning activities. From observations on the process 

 in both cases the author concludes that in this species polar bodies and 

 egg are physiological, as well as morphological, equivalents, and, from 

 the activity of the polar bodies, it may be said that the oogenesis shows a 

 much closer morphological equivalence to spermatogenesis than is usual. 

 Segmentation is total and equal, and during it the spin-threads connect 

 the blastomeres and prevent physiological separation. Gastrulation is 

 embolic, and is speedily followed by the development of the apical plate 

 and a covering of cilia. The pilidia were reared in large numbers, and 

 were studied in the living condition. As they are exceedingly transparent, 

 observations could be readily made on the origin of the muscles. It 

 was found that the muscles of the pilidium are metamorphosed pseudo- 

 podia, the metamorphosis consisting essentially in a fibrillation of a 

 portion of the cytoplasm and the gradual assimilation of the remainder. 

 The fibrillation appears to begin in a rearrangement of the cytoplasmic 

 reticulum, and occurs only when the pseudopodium has attached itself 

 to something outside the cell. 



For histological work, platinum chloride was found to be the best 

 preservative, used either alone or with acetic acid. An important point 

 in regard to histology is the apparent absence of any nervous tissue in 

 the apical plate. 



Coelentera. 



Longitudinal Fission in a Sea-Anemone.* — Mr. G. H. Parker sum- 

 marises the evidence which leads him to believe that specimens of 

 Metridium marginatum with double discs are not monstrosities, as has 

 been supposed, but cases of incipient division. The process apparently 

 produces monoglyphic or irregularly diglyphic specimens, and not 

 regular hexamerous diglyphic specimens. It would appear that the 

 latter must be the products of sexual reproduction, as there is no evidence 

 that they can result from non-sexual processes. Such regular specimens 

 constitute about one-fifth of all collected. 



Medusae of Millepora.f — Prof. S. J. Hickson, who discovered male 

 medusae in specimens of Millepora collected by H addon in Torres 

 Straits eight years ago, has now obtained immature and mature female 

 medusae from Jamaica, where Mr. J. E. Duerden actually saw them 



A Bull. Mus. Comp. Zool. Harvard, xxxv. (1899) pp. 43-5U (3 pis.). 

 T Proc. Roy. Soc, lxvi. (1900) pp. S-10 (10 figs.), 



