ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 15 



Especially lie notes that the spiral thread of the mammalian sperm is 

 formed of mitochondria, and is therefore the equivalent of the envelope 

 of the middle-piece, and so of the Nebenkern of Invertebrates. He 

 figures various structures liable to be mistaken for mitochondria or 

 mitochondrial corpuscles, notes that they may both occur in other cells 

 besides spermatozoa, e.g. in Sertoli's cells in the testes of Vertebrates, 

 and discusses the question whether the mitochondria are to be regarded 

 as identical with the microsomata of tissue-cells. This last point, as 

 well as the question of function, is left undecided. 



Fertilisation in Petromyzon fluviatilis.* — Dr. Karl Herfort has 

 studied the maturation and (artificial) fertilisation of the eggs of the 

 lamprey, and gives his general results as follows. In all stages of the 

 egg foam-structure of the cytoplasm in Biitschlrs sense was clearly 

 detected. The same structure was made out in the spheres and their 

 radii, while no indication of contractile threads in the sense intended 

 by Van Beneden, Boveri, &c. was observed. The sperm-head, before it 

 is reconstructed as a pronucleus, consists of a group of small vesicles 

 which are identical with Platuer's karyosomata. The sperm-sphere 

 seems to arise from the cytoplasm of the egg. The sphere lies in the egg 

 behind the sperm-head, and when the latter becomes a pronucleus, the 

 sphere becomes elongated and spindle-shaped, and the central corpuscle 

 divides, a division which is followed by that of the sphere. The two 

 spheres form the poles of the first segmentation spindle, and at the 

 metaphase increase greatly in size, probably constituting the coarsely 

 alveolar area which surrounds the daughter-nuclei. The author believes 

 that the daughter-spheres are new formations here as elsewhere, while 

 the central corpuscles are to be regarded as permanent organs. As a 

 remarkable and as yet inexplicable fact, the author notes that the male 

 pronucleus is at one stage surrounded by a clear area into which the 

 female pronucleus also migrates. He believes that it is not an artefact, 

 but can say nothing of its origin, fate, or relations. 



Foetal Membranes of Dasyurus. f — Mr. J. P. Hill has found that 

 Dasyurus viverrinus will live and breed in captivity, and he has therefore 

 been enabled to study the placentation and process of parturition in great 

 detail. The present note contains a preliminary account of his results. 

 The period of gestation appears to be about eight days, which agrees 

 with Selenka's observations in the case of the opossum. As in other 

 Marsupials the wall of the embryonic vesicle is divided into three 

 zones : — (1) The bilaminar omphalopleure — forming here the larger 

 part of the wall ; (2) the true chorion ; and (3) the trilaminar omphalo- 

 pleure. An important point is that the proamnion, transitory in the 

 Australian forms hitherto described, is here, as in Didelphys, persistent, 

 and invests the embryo up to the fore-limbs. In regard to size, the 

 allantois is well developed, but the shape is peculiar, being band-like 

 with no definite stalk, and the vessels are degenerate, a large part of the 

 area even in the early stage showing no trace of blood-supply. Never- 

 theless the allantois makes an abortive attempt to fuse with the chorion. 

 The yolk-sac placenta is somewhat complex, and consists of two parts 



* Arch. Mikr. Anat., lvii. (1900) pp. 54-95 (3 pis.). 

 t Anat. Anzeig., xviii. (1900) pp. 364-73 (1 fig.). 



