PROGRESS OF MICROSCOPICAL SCIENCE. 185 



regarded the membrane in question in tlie Mites as homologous with 

 the larval membrane of the Crustacea, and the latter as homologous 

 with the " insect-amnion," for which he has elsewhere proposed the 

 better name of " protoderm." Shortly after the formation of the em- 

 bryonal envelope, we see, between it and the blastoderm, the first 

 amceboid cells (licemamoebce of Claparede). He remarked that these 

 cells " are blood corpuscles of quite abnormal derivation." In using 

 this expression he had the circumstance in his mind that they are 

 formed from separated blastodermic cells, which, at the time of their 

 production, are the sole cellular structures that are found in the egg. 

 He did not then feel it necessary to say anything more upon this 

 point, as the publication of his original memoir was to be expected. 

 He thought at first that the blood corpuscles were all developed from 

 separated, blastodermic cells, and only afterwards, perhaps after the 

 formation of the buccal orifice, passed through this into the embryo. 

 As, however, he never saw any such migration of the cells, even after 

 observing them for hours, he has given up this view, and now thinks 

 that there is a further formative focus for them in the interior of the 

 embryo. His present opinion as to the hasmamoebte is, that they really 

 agree perfectly in form and behaviour with blood corpuscles, but 

 nevertheless cannot be regarded as blood corpuscles. He sees in 

 them ajipurtenances of the embryonal envelope which Claparede 

 denominates the deufovum. Whilst at the commencement of embry- 

 onal development of many insects a cellular envelope separates from 

 the blastoderm, and in some Crustacea a larval skin, which is usually 

 structureless, in Atax a larviform structure first separates from the 

 blastoderm, and shortly afterwards the contractile cells. This state 

 of things, when regarded in this manner, fui'nishes an additional 

 reason for regarding the embryonal envelope of Atax as the homo- 

 logue of the protoderm of insects. 



Observations of Pachytragous Sponges. — Some observations of an 

 interesting character have recently been made by Mr. H. J. Carter, 

 F.E.S., on certain sponges from the south coast of Devon. The chief 

 point of interest in these sponges — Dercitus niger, Stelletta aspera, and 

 S. lactea — is the presence of peculiar cells in Dercitus niger and Stel~ 

 letta aspera, corresponding in multiplicity, position, and general dis- 

 tribution, though not in composition, to the globular crystalloids or 

 little silicious balls in the crust and body of the Geodidas ; add to 

 this their contents, which render them so much like reproductive 

 agents, and, lastly, their occurrence in the two sponges mentioned, 

 and not at all in the thii-d, viz. Stelletta lactea. Nor do they exist in 

 Pachymatisma Johnstonia ; but in the dried specimens of Geodia gigas, 

 presented to the British Museum by Dr. Oscar Schmidt, there are 

 similar cells in abundance, together with the globular crystalloids. 

 Although analogous in multiplicity, position, and distribution to the 

 globular crystalloids in the Geodidae, they not only diflfer from them, 

 as just stated, in composition, by the former being cellular and albu- 

 minous, while the latter are solid and silicious throughout,* but also in 



* ' Annals of Natural History,' 1869, vol. iv., p. 16, &c., pis. 1 and 2, figs. 12 

 and 14. 



