488 SUMMARY OF CUB-RENT RESEARCHES RELATING TO 



lations are to be seen within the substance of the nnclens. In others 

 the black granulations are so richly developed as to completely 

 obscure the nuclear mass, although that body is still present- 

 Finally the cells commence to undergo degeneration, their membrane 

 breaks, and the pigment escapes ; the nucleus, however, still persists, 

 and it is in consequence of this that we find free nucleated masses 

 in the midst of the pigmented granulations. The author discusses in 

 order the histological characters of the meshwork, the wall of the 

 pouch, its internal, median, and external tunics. 



Turning to the development of the ink-sac, we find that on the 

 fourth day of the second period (that of the development of the 

 organs) the anal depression comes in contact with a process of the 

 mesoderm, and then divides into two portions, the superior of which 

 is the ink-sac, and the inferior the rectum. The former rudiment has 

 at first a transverse direction, and extends from the anal orifice to the 

 internal yolk-sac, and is clothed by a single layer of epithelial (ecto- 

 dermic) cells. This is what will form the vesicle. The cells at 

 the caBcal extremity soon begin to multiply and form a thickening 

 which is the rudiment of the gland. The glandular mass developes 

 rapidly by making its way into the midst of the mesoderm ; the cells 

 of that layer now begin to form peripheral layers around the gland, 

 till they nearly completely surround it, and the mass becomes 

 divided into two lobes, between which there is an extension of the 

 mesoderm. Changes in the cells themselves now appear, and give 

 rise to the formation of a thick granular liquid. As soon as the 

 glandular cavities are developed the investing cells take on the 

 characters which belong to the formative zone of the adult, and a 

 peripheral and a formative zone are thus developed. Further changes 

 bring about a connection between the gland and the reservoir ; the 

 latter then begins to increase rapidly in length, and at the same time 

 to dilate. Still further changes, in the mesoderm, give rise to the 

 different investing layers, and there is some alteration in position. 

 Looking more generally at the matter, we find that the ink-sac is 

 formed by an epidermal invagination, which, during development, is 

 differentiated into two parts, the gland and the vesicle (reservoir); 

 this invagination is contained in a kind of mesodermic sac, which 

 forms the tunics that envelope the epithelium ; the innermost of these 

 consists of an epithelial and of a connective layer, the median of the 

 silvery and of a muscular layer, and the outer of connective tissue. 

 "When we compare this with the integument, we cannot but be struck 

 with the remarkable similarity between them ; there, too, we find an 

 epithelium, the cells of which are arranged in a single row, and 

 limited externally by a thick cuticle ; the connective layer contains 

 the chromatophores, and beneath this there are a silvery layer, 

 muscular fibres, and a layer of connective tissue. The absence of 

 chromatophores in the region of the sac may be explained by a study 

 of the intermediate stages presented by different parts of the body. 



The researches of Lacaze-Duthiers on the purple-glands of certain 

 Gastropoda have led the author to make a study of these structures, 

 from which it results that their anal gland is homologous with the 



