572 SUMMAKY OF CURRENT RESEARCHES RELATING TO 



skeleton is only found in very young buds and afterwards disappears, has 

 been led to reconsider tbis. He now finds tbat in Farella repens, and 

 another species, probably a Membranijpora, there is on the surface of the 

 tegumentary skeleton a thread indicating an epithelium formed of very 

 large cells ; these cells closely resemble the ectodermal cells of Loxosoma 

 and PedicelUna ; it is very difficult to detect this layer except in specimens 

 which, when fresh, have been treated with nitrate of silver. 



The author's researches on Flustra have shown him that the endocyst 

 and endosarc are formed of the same non-epithelial tissue ; tbis parencby- 

 matous tissue appears to be a special form of connective tissue which is 

 massive in the cords and reticular in the layers which line the cavity of 

 the body. In Bugula calathus it often contains a number of spherical or 

 ellipsoidal corpuscles, which are granular in appearance ; they vary greatly 

 in their distribution. They multiply by division, and tbis is better seen 

 in buds than in adults ; their function seems to be tbat of formative 

 elements, wbicb serve eitber to nourish the tissues or to give rise to new 

 cells in developing individuals, helping to form new organs. The muscular 

 fibres are only these cells excessively elongated. 



There can be no doubt that in the budding of the ectoproctous marine 

 Bryozoa two distinct and well-developed embryonic layers take a part ; the 

 outer one is composed of large cells, in which the tegumentary skeleton is 

 deposited, and the inner invests the cavity of the young bud and furnishes 

 nearly the whole of the organs and tissues of the adult ; in consequence of 

 its situation and the part it plays in development it must be regarded as 

 representing the mesodermal lajer. In the early stages it forms an epi- 

 thelium, which does not persist, but is converted into ovicells or avicularise, 

 or furnishes the different organs which fill the cavity of the bud ; it also 

 provides the materials for the development of the nutritive apparatus. In 

 tbis last both ectoderm and mesoderm take a share. If it be admitted that 

 the endoderm is wanting, then the epithelial layer which invests the cavity 

 of the young bud ought to be considered as representing both mesoderm 

 and endoderm ; from the time of the formation of the gastrula the elements 

 of the inner layer are fused with the internal cellular mass of tbe embryo. 



Morphology of Marine Bryozoa.*— Dr. W. J. Vigelius gives a pre- 

 liminary notice of bis results with regard to tbe morphology of ecto- 

 proctous marine Ctenostomatous and Cyclostomatous Bryozoa. The 

 ectodermal epithelium has been studied by silver preparations of Bugula, 

 Memhranipora, Flustra, and Mimosella ; in tbe adult of all it consists of 

 large, much-flattened cells, and in the rudiments of the bud of smaller 

 polygonal cells. Contrary to Kohwey, Dr. Vigelius believes that tbe fine 

 partition-walls which separate the individuals of Alcyonidium from one 

 another are perforated, and so correspond to the communication-plates 

 which are so often found in the Ectoprocta. 



With the exception of Alcyonidium all the forms examined had tbe 

 parenchymatous tissue developed on one and the same type ; and tbis 

 closely corresponds to what the author has already found in Flustra mem- 

 hranaceo-iruncata and Bugula calathus. The nutrient apparatus is very 

 much the same in all forms ; the cilia of the tentacles of preserved speci- 

 mens were seen to be arranged in the same way as in Flustra ; Zoobotryon 

 and Mimosella, in addition to the pharynx, stomach, c^cum, and intestine 

 of other forms, have a masticatory stomach. The circular canal is always 

 found, and is invested by the continuation of the mesenchymatous layer 

 which is found in tbe tentacular canal ; in Alcyonidium mytili the author 



* Zool. Anzeig., x„ (1887) pp. 237-40. 



