ZOOLOGY AND BOTANY, MICKOSCOPY, ETC. 179 



polar globules, among others. An alphabetical bibliograpbical list, 

 and a list of the authors cited in tbe text aids the reader in his study 

 of the work. 



The eggs, usually found in clusters of about a dozen, vary in 

 their mode of packing, and in their arrangement in the cracks of earth 

 which shelter them ; their more or less plump appearance depends on 

 hygrometric conditions, and they are not always of the same form. 

 When first deposited, the yolk is much denser than the surrounding 

 albumen, but it is not provided with any proper vitelline membrane. 



At first the changes occur very slowly, but soon they succeed 

 one another more rapidly. First one and then the second polar 

 globule appears, and, as a rule the latter is somewhat smaller. In 

 dealing with the formation cf the female pronucleus, the author 

 points out that it constantly remains near the surface of the vitellus ; 

 its diameter may eventually attain one-fourth the diameter of the 

 whole vitellus, or, in some cases, one-third. When treated with 

 acetic acid, the female pronucleus is modified in shape by the forma- 

 tion of a number of deep wrinkles and folds ; when with osmic acid 

 (and subsequent staining in carmine), it has a delicate and even 

 outline, and its form is spherical, pyriform, or oviform. Soon after 

 extrusion, a number of small ovoid bodies of high refractive power 

 are to be found near the vitellus, presenting a filamentous appearance 

 in some cases ; they are, doubtless, all spermatozoa ; they may be 

 present in great quantities, and even form " trains " through different 

 parts of the albumen. In one case an undulating membrane was 

 noted in a spermatozoon. 



After dealing with the characters of the male pronucleus and its 

 history, the author passes to cleavage; here he finds that the first 

 cleavage nucleus does not have a morphological existence ; this is 

 explained by assuming that the acceleration at this stage of the 

 ontogeny is so great that the division of this future structure is begun 

 before it has an actual independent existence. He is further of 

 opinion that a differentiation commences in the superficial portion 

 of the yolk, which is the first step toward the formation of a cell- 

 membrane, and that this differentiation is proportional to the advance 

 of cleavage. 



It is impossible to enter into the details of the elaborate account 

 of previous naturalists' observations which form the great bulk of 

 this communication, which was apparently in the press before the 

 publication of Mr. Balfour's systematic treatise. 



Kidney of Chiton.* — Mr. A. Sedgwick gives an account of the 

 structure of the kidney of Chiton, which is a paired gland constructed 

 on the type always found in molluscan renal organs. It consists of — 



1. A duct opening to the exterior in the pallial groove behind 

 the generative opening, and internally into the pericardium. 



2. Glandular caeca opening into this duct. 



The duct may be described as consisting of three parts : — (1) 

 The part into which the glandular cfeca of the kidney open. This 



* Proc. Eoy. Soc, xxxiii. (1882) pp. 121-7 (2 figs.). 



N 2 



