906 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [16] 



eduUs. We therefore fiDcl in this fact another proof that, phylogenet- 

 ically, the filamentons branchiae represent a former stage, and the la- 

 mellar branchiae a later one. 



A no less important question is to ascertain how the oyster becomes 

 fixed. It is known that some bivalve moUusks are fixed during their 

 entire life by means of the byssus; others, on the contrary, like Hin- 

 nites, the Spondylvs, &c., use this means only temporarily; and later 

 their shell is firmly soldered to the object on which they are found. As 

 the oyster becomes fixed at an early age, it becomes necessary to place 

 the animal with the object to which it adheres (in short, the "collector") 

 under the microscope, care being taken that it remains intact. 



Mr. Eyder,^^ in "An account of Experiments in Oyster culture, &c.," 

 recommends to obtain for this purpose larvae attached to cotton threads 

 or to pieces of mica or glass. There is no doubt that among the sub- 

 stances mentioned by him glass will be the only one by which the object 

 in view can be reached; for if the collector is opaque, microscopic ob- 

 servations by means of transmitted light become impossible and may 

 l)rove the cause of great difiiculties, I conceived the idea of using as 

 collectors the glass slides used for mounting microscopic objects, and I 

 was confirmed in this idea after having read an article by Prof. Karl 

 Mobius in the ZooUxjischer Anzeiger of January 22, 1883. In order to 

 j)rocure living auimalculae for his microscopic observations he placed 

 the ghiss slides in a wooden frame, which he put in the water about two 

 feet above the bottom of the sea. A number of animalcules, such as 

 Polyps, Hydroids, Bryozoans, Infusoria, &c., adhered to the slides so sup- 

 ported. 



The apparatus used by me, which has worked very successfully, 

 is composed of a series of woodeu frames or bars, on the upper and 

 lower edges of which a double row of small notches is cut, and in 

 each of which a piece of a glass slide may be inserted. The central 

 bar is provided with lateral notches, which makes it easy to take out 

 the slides, while on the outer side a little peg holds it in place. On the 

 lower side of the frame there is an iron band, which makes the apparatus 

 heavier and prevents it from floating, while on the lower side of the 

 ui)per edge there is a projection, which makes it possible to rest the col- 

 lector on some support, so that a current of water may pass underneath. 

 It was my intention to place this collector among the tiles used in the 

 Netherlands for gathering the spawn of the oyster, so as to make my 

 observations as much as possible under the same natural conditions. 



The length of the collector is 210 millimeters [about 8^ inches] — that 

 is, almost the length of a tile — while its breadth is 180 millimeters 

 [about 7 inches], so that on each side of the frame there may be placed 

 six glass object-holders (English size). As it was to be feared that the 

 larvae would not adhere to common glass on account of its being smooth, 

 some of the pieces of glass were ground rough ; others were covered 



23 Report of Ferguson, Commissioner of Fisheries of Maryland, 1881, p. 57. 



