286 



NATURE 



[July 23, 1896 



aluminium 25, leail 0'29, gold o'28, and plalinum 2^. The 

 author also found a slight difference between the transparency 

 of solid substances and their powders, which shows that there is 

 some reflection or refraction. Loose powder was even less 

 transparent than pressed powder. 



SOCIETIES AND ACADEMIES. 

 London. 



Royal Society, May 21. — "Note on the Larva and Post- 

 larval Development of I.eiuosolenia variabilis H. sp., with 

 Remarks on the Development of other Asconida;." By E. A. 

 Minchin. 



The larva of Leucosolenia variabilis is an amphiblastula of a 

 primitive type, transitional in many respects between the larva 

 of the lower Ascons and the amphiblastula of the Sycons. It 

 has an anterior ciliated, and a posterior non-ciliated pole, but 

 when first hatched the ciliated pole is relatively very large, and 

 the non-ciliated cells are few in number. During the free- 

 swimming larval period the non-ciliated cells increase through 

 their numbers being recruited from the ciliated cells, of which 

 tho.se situated more posteriorly become modified into granular cells 

 after passing through an intermediate stage. In addition to 

 anterior ciliated cells, po.sterior granular cells, and the equatorial 

 zone of intermediate cells, the larva has cells of a fourth kind, 

 placed in the centre of the body, immediately behind the minute 

 central cavity, which contains gelatinous matter and is surrounded 

 laterally by a ring of pigment lodged in the inner ends of the 

 ciliated and intermediate cells. The central cells, together with 

 the pigment, appear to constitute a larval organ, perhaps 

 sensitive to light, which is lost at the metamorphosis. 



The larva swims for 36-48 hours and fixes by the anterior 

 pole. The granular cells grow round the ciliated cells, and the 

 former become the dermal layer, the latter the gastral layer. At 

 first the dermal layer forms an epithelium of a single layer, which 

 becomes two-layered by immigration of certain of its cells. The 

 dermal cells which remain on the siirface secrete each a single 

 monaxon spicule ; those which migrate inwards arrange them- 

 selves into groups, and secrete the tri- and quadri-radiate spicules. 

 While these changes are taking place in the dermal layer, a 

 central cavity has appeared, round which the gastral cells arrange 

 themselves in a columnar epithelium and gradually assume the 

 characters of collar cells. At one spot the cavity is not lined 

 by gastral cells, but by dermal cells only ; it is here that the 

 osculum is formed about the sixth day of fixation. 



In the other Ascons investigated — L. cerebrum, L. coriacea, 

 and L. reticulum — the larvoe are oval ciliated blastuke in which 

 an inner mass of cells is formed by modification and subsequent 

 immigration of certain of the ciliated cells. In cerebrum and 

 coriacea the immigration appears to be multipolar ; in reticulum 

 it takes place from the posterior pole, and thus affords a transi- 

 tion to the above-described larva of variabilis. If the cavity of 

 the larva of reticulum be imagined reduced to the extent to 

 which this has occurred in variabilis, then the modified cells at 

 the hinder pole, instead of migrating inwards, must remain 

 where they are, and as more ciliated cells become modified 

 around them, a type of larva is obtained with ciliated cells 

 anteriorly, intermediate cells laterally, and non-ciliated cells 

 posteriorly, as in variabilis. This homology is further borne 

 out by the fact that in all these larva; the inner mass becomes 

 the dermal layer, and the ciliated cells become the gastral layer, 

 as the result of changes in position which take place at the 

 metamorphosis. The post-larval develojiment of the layers- is 

 similar to that described for variabilis. 



When the development of /,. variabilis is compared with that 

 of Sycon as described by Schulze and Metschnikoff, it is seen 

 that the only difference between them lies in the ]ieriods at 

 which the events take place. In Sycon the larva, while still in 

 the maternal tissues, undergoes changes which in variabilis take 

 place during the free-swimming period, and the dermal cells 

 surround the gastral cells before fixation in Sycon, instead of 

 after fixation, as in variabilis. 



The primitive larva of Calcarea was probably a ciliated 

 blastula, in which an inner mass, the future dermal layer, was 

 formed by modification and immigration of certain of the cells. 



The immigration of cells from the dermal layer to form 

 the triradiate spicules is precisely similar to what occurs in the 

 adult whenever new spicules arise. Mence this process is not to 



NO. 1395, VOL. 54] 



be regarded as one of blastogenetic, but of histogenetic signifi- 

 cance. In other words, sponges are to be regarded as two- 

 layered animals, and not as possessing a mesoderm. 



June 18. — '*On Fertilisation, and the Segmentation of the 

 Spore, in I'ucus. By Prof. J. Brclland Farmer and Mr. J. LI. 

 Williams. 



An account was given of an investigation into the mode of 

 formation of the oospheres, of their fertilisation by the 

 antherozoids, and of the germination of the resulting spores in 

 various members of the Fucaceie, special attention being paid 

 to the protoplasmic structures therein concerned. The chief 

 points were illustrated by lantern-slides from photomicrographs. 



In order to study the fertilisation and germination stages, 

 dioecious .species were selected, and the male and female plants 

 were kept in separate dishes, covered over so as to prevent dry- 

 ing up. This method gave far better results than those more 

 usually advocated. On the appearance of the extruded sexual 

 products, the female receptacles were placed in sea water, and 

 after the complete liberation of the oospheres, a few male 

 branches with ripe antherozoids were first jilaced in a capsule of 

 sea water until it became turbid owing to their number. If on 

 examination the antherozoids proved to he active, small quanti- 

 ties were added to the vessels containing the oospheres. The 

 latter were then fixed at intervals of five minutes during the 

 first hour, and then at intervals of fifteen minutes, up to six 

 hours after the addition of the antherozoids. After that, sam- 

 ples were killed at longer intervals up to three days, and this 

 was continued till we had material fixed at all stages for the 

 first fortnight. At first sea water was used in which to keep the 

 embryos growing, but a proper solution of Tidman's sea salt 

 was found to answer quite as well. A large number of fixing 

 reagents were tried, but Flemming's solution diluted with sea 

 water gave the best results. Many reagents in common use 

 proved utterly worthless. In embedding the tissues and spores 

 in paraflin, previous to cutting them, it is important not to allow 

 the temperature to rise above 50° C 



When an oogonial nucleus is about to divide, it first becomes 

 slightly, then very much, elongated so as to resemble an ellipse. 

 Fine radiations are seen to extend from the two ends into the 

 surrounding cytoplasm. The latter is at first tolerably uniformly 

 granular, but as the radiations around the polar areas increase, 

 these regions become cleared altogether of the granules which 

 then become massed outside them. The nucleus rapidly becomes 

 more spindle-shaped, and its chromatic elements are chiefly 

 grouped near each pole, leaving a clear space about the equator 

 in which the nucleolus is situated. 



The polar radiations continue to increase and the nucleus to 

 lengthen, until the entire structure recalls the figure of a dumb- 

 bell, in which the nucleus answers to the handle, and the radia- 

 tion areas to the knobs. If the radii be traced outwardly, they 

 are seen to terminate either in the frothy protoplasm, on the 

 angles where the foam walls meet, or on the large granules 

 which surround the cleared areas and are embedded in the foam. 

 No structures were seen which could certainly be identified as 

 centrosomes, although bodies suggestive of them were often 

 observed ; but these proved to be .so variable in size and posi- 

 tion, as well as in number, that it appeared impossible to attach 

 any special .significance to them. 



The achromatic spindle is remarkable, inasmuch as it is 

 intranuclear. The chromosomes were too minute to admit of 

 their development being satisfactorily studied, but in all the 

 O0j{iiiiial spindles the number was estimated as teu when seen in 

 profile. .-Vfter the delimitation of the oospheres, some of them 

 were observed to contain more than one nucleus. This is an 

 abnormal feature, and the non-recognition ol this fact has led to 

 mistaken views in the past. When the oospheres are extruded, 

 and come to lie free in the water, they swell somewhat, and are 

 turbid with granules, which are very abundant in the cytoplasm. 

 About five minutes after the mixing of the sexual cells, the 

 antherozoids are found to have slippad into many of the 

 oospheres. The act of penetration was not observed, but, in a 

 number of cases, the anthernzoid could be recognised within the 

 oosphere, before its final fusion with the nucleus of the Utter. 

 It is a roundish, den.iely staining body, and, unlike the majority 

 of animal sperm cells as yet described, no system of radiations 

 are associated with it when in the egg. Judging from the short 

 period of time ela])sing between its penetration of the surface of 

 the oosphere and its arrival at the exterior of the female nucleus, 

 it must pass through the intervening cytoplasm with great 

 rapidity. It then becomes closely appressed to the nucleus, 



