INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 77 



Development of Moina rectirostris.* — After giving an account 

 of the development of this form, Dr. Grobben enters into a considera- 

 tion of the anatomy of the Phyllopoda. In the earliest period of 

 development we have to do with a very small egg, the protoplasm 

 of which is more finely granular at the animal pole ; the nucleus is 

 placed rather nearer to this pole, but there is, in addition to the 

 nucleus, another body, small and more or less rounded, which 

 presents the same tinge with carmine as the nucleus, and appears to 

 be a part of the ovarian nucleus, which, while being converted into a 

 directive corpuscle, is making its way towards the periphery. The 

 nutritive yolk consists of a few refractive, almost colomdess, spheres 

 and a layer of small granules, which are set amongst the spheres, 

 which, red, blue, or violet in colour, make up the greater part of the 

 yolk. Cleavage soon commences after the eggs are laid, and, as 

 ordinarily, commences by a division of the nucleus. A meridional 

 groove appears on the surface of the egg, and the yolk material 

 begins to take up a central position, and neither this nor the next 

 succeeding divisions succeed in completely separating the yolk into 

 separate cells ; in other words, cleavage is superficial. At the stage 

 of cleavage in which there are seventeen cells, it is possible to see a 

 central one, which is coarsely granular, and which, from its future 

 history, may be called the genital cell. Shortly after this the 

 endodermal cells can bo seen to be eight in number, and to be smaller 

 than those of the ectoderm. Passing on to the gastrula stage, we 

 find in optical section a layer of cylindrical cells pushing their 

 way into the blastocoele and connected at one point with two 

 large genital cells, and at another with five cells, which belong 

 to the mesoderm ; the greater part of the blastula-cavity is occupied 

 by the food-yolk. "When the gastrula mouth closes the genital 

 cells leave their position near it to pass inwards and under the 

 endoderm. 



In the second period of development tlie small egg begins to 

 grow, and the greatest increase takes place in the cells of the 

 mesoderm, which now extends not only as far forwards as the frontal 

 plate, but along the sides and over the whole of the ventral surface ; 

 the largest of its constituent cells are to be found in the hindermost 

 region ; the genital cells form a bilaterally symmetrical plate below 

 the endoderm. Soon the embryo becomes divided into two portions ; 

 the anterior one becomes the cephalic segment, wliile the posterior 

 forms the rudiment of the trunk. On cither side of the former there 

 appears an car-shaped process, which is tlie rudiment of tlio second pair 

 of antcnufe ; the mouth forms a small depression between them. As 

 the hinder portion grows, a new segment is nipped oft" at its anterior 

 end, on which there soon ap])car the rudiments of the mandibles. 

 The Naiij'lins stage is now reached ; into the details of the arrange- 

 ment of all the parts of the embryo it is impossible to enter, but it 

 may be noted that the ecdysis which obtains in so many allied forms 

 is not seen in Moina ; probably, as Dr. Grobben thinks, because tho 

 creature swims in albuminous matter, and the preseucc of a second 

 * 'Arbeit. Zool. lust. ■\Vurzl.urg,' ii. i,lS7'.<) p. 20.3. 



