ZOOLOGY AND BOTANTj MICROSCOPY, ETC. 735 



the genital segments, was found to contain encysted Gregarines in the 

 pseudo-navicella-stage, which resembled the Monocystis of Lumhricus. 



Dr. Collin agrees with Eosa in believing that Criodrilus has close 

 systematic affinities to the Lumbricidse. Eosa's views are supported by 

 Benham's discovery of the clitellum. 



Formation of Embryonic Layers and Coelom of a Limicolous 

 Oligochsete.* — M. L. Eoule has investigated the earlier stages in the 

 development of Enchytrseoides Marioni (sp, n.). The nutrient yolk, 

 though abundant, is distributed uniformly through the egg, and the first 

 two blastomeres are, consequently, almost equal. Afterwards segmenta- 

 tion is very irregular, but the germinal does not separate from the 

 nutrient yolk and develope much more rapidly. In the morula-stage 

 the outer cells form the ectoblast, and the inner the meso-endoblast ; of 

 the latter the central cells will give rise to the endoblast. There is 

 no definite blastoccel. 



At the end of the morula-stage a cavity, which is at first irregular, 

 appears in its centre ; this is the first indication of the digestive cavity ; 

 the cells which surround it become cylindrical. As the digestive cavity 

 increases in size spaces appear in the mass of mesoblastic elements ; 

 these spaces fuse with one another, and there is thus formed a cavity 

 which divides the mesoblast into two layers, and which will become the 

 coelom. At no period was it observed to communicate with the enteric 

 cavity. As the embryo grows the coelom increases in size ; the inner- 

 most cells of the parietal layer of mesoblast proliferate, and some become 

 free in the cavity, where they produce the formed elements of coelom ; 

 others remain in their places and advance towards the visceral mesoblast, 

 with which they fuse ; in this way the septa which separate the 

 segments are produced. Others of the cells of the parietal layer of the 

 mesoblast elongate, secrete a contractile substance, which accumulates 

 round the protoplasm which surrounds the nucleus, or become smooth 

 muscular fibres. This mesenchymatous origin of the muscular fibres is 

 comparable to what happens among the Mollusca ; it and the absence of 

 initial mesoblast-cells are facts which appear to be explicable by the 

 abundance of nutrient yolk, and they must be set against the existence 

 of initial mesoblast-cells in most chsetopod Annelids, and the epithelial 

 origin of the muscular tissue of the adult in the Arehi-annelids. 

 It is clear from these considerations that the more or less large 

 quantity of yolk has an influence on the mode of development of the 

 germinal layers and of the tissues, and that consequently we cannot base 

 the embryo-genetic relations of animals solely on their histogenetic 

 characters. 



Nephridia of Lanice conchilega.t — Mr. J. T. Cunningham gives an 

 interesting account of the excretory system of Lanice concMlega 

 Malmgren. It consists of eleven nephridia, three rudimentary, in 

 somites 3-5 ; four perfect, in somites 6-9 ; and four imperfect, in 

 somites 10-13. The eight posterior nephridia communicate with each 

 other by means of a longitudinal tube formed by the fusion of their 

 distal parts. " This," Mr. Cunningham concludes, " is the first case in 

 which such a longitudinal coalescence of nephridia has been discovered, 

 and its morphological similarity to vertebrates is obvious." 



* Comptes Eendus, cvi. (1888) pp. 1811-13. 

 t Proc. E. So3. Edin., xiv. (1887) p. 238. 



