ZOOLOGY A^^D BOTA^TT. IIICKOSCOPT, ETC. 727 



ntunber of secondary infunclibnla will be found to have greatly in- 

 creased, more than 500 being now present. The author points out 

 that the presence of more than one excretory orifice obtains in th.e 

 Cestoda and Trematoda, and that if the observations of Hatschek are 

 correct, Polygordius commences with a renal organ which has a single 

 orifice, and only secondarily gets a series of orifices. If M. Julin's 

 studies are corroborated, we shall have in the hypophysial gland of 

 the Tunicata the primitive renal organ of the Chordata. 



Coelom of the Ascidians.* — Professor E. van Beneden states 

 that the mesoderm of the larva is formed by two lateral plates, which 

 are fonned solely in the posterior haK of the embryo and at the 

 expense of the endoderm ; the hinder half of each gives rise to the 

 muscle-cells of the tail ; the anterior encloses a cavity which seems to 

 be a lateral diverticulum of the archenteron, or, in other words, an 

 enteroccele. The cells of the anterior half of the mesodermal plates 

 become rounded, separate from one another, and take on the character 

 of blood-corpuscles. 



In the adult Perophora the heart is formed by a single layer 

 of cells, the deeper parts of which liave their protoplasm ti-ans- 

 formed into muscular fibrillas. The generative organs and their 

 ducts are developed at the expense of a small mass of mesodermic cells, 

 in -which there appears an excentric cavity which by growth gives rise 

 to a sexual vesicle ; this divides into two lobes, of which the outer one 

 forms the female and the inner the male organs. The author finds a 

 very close analogy between the development of the pericardium and 

 that of the sexual vesicle. " If the pericardiac cavity is the homo- 

 logue of that of Yertebrates, the cavity of the sexual organs is the 

 homologue of the abdominal cavity. They both have the characters of 

 a true ccelom," and the mouths of the efferent ducts appear to repre- 

 sent abdominal pores. The enteroccele of the larva disappears 

 completely, and the bounding epithelial cells give rise to a true 

 mesenchyma. 



Professor van Beneden tas noticed that the muscles of the Asci- 

 dians, and even the mode of the termination of the nerves in the 

 muscle, resemble the smooth fibres of the Yertebrata. 



Metamorphosis of PedieelliiLa.t — M. J. Barrois finds that this 

 Polyzoon becomes fixed by the oral, and not by the aboral, pole of its 

 body. The digestive tube is rotated from before backwards, when the 

 intestine ceases to have a horizontal position and passes through two 

 stages. In the first, which is analogous to what is seen in Loxosoma, 

 the enteron is vertical, and its orifices look towards the posterior sur- 

 face of the larva ; in the second the enteron is horizontal, and its 

 orifices are directed upwards. The vestibule meantime becomes 

 divided into three distinct parts ; the lowest contains elements which 

 go to form the foot-gland ; the uppermost forms the tentacular 

 chamber, and comes into connection with the exterior by means of an 

 invagination of the ectoderm ; the median portion undergoes degenera- 



* Zool. Anzeig., iv. (ISSl) pp. 375-S. 



t Comptes Eendus, xcii. (1881) pp. 1527-8. 



