772 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [10] 



through the jar. Some are visible with the edges turned towards the 

 observer and open and close their valves at intervals. Even the ciliary 

 action and protrusion and retraction of the velum is often apparent. 

 The attempt to discover a byssal attachment was fruitless. I usually 

 found such an amount of sediment and slimy matter in the vicinity of 

 the embryos as to prevent me from making out anything of a definite 

 and positive character in regard to this point. The water still remains 

 pure however ; no signs of any putrescent action are yet apparent. The 

 cotton filter has been of great use to us. In order to discover whether 

 the attachment of the embryos was accidental or weak, Colonel Mc- 

 Donald detached one of the jars from the circuit and caused a contin- 

 uous current of water to flow through it. This showed that the attach- 

 ment was pretty firm; the current so established through the jar did 

 not detach the embryos, as we could see by examining the inner sur- 

 face of the glass jar with our microscope extemporized for that purpose. 

 The temperature of the water to-day has ranged from 74° to 88° Fahr. 



July 24.— Colonel McDonald has arranged a second set of jars and 

 aquaria similar to the first, with the exception that the oyster shells have 

 been purposely omitted in order to learn whether their presence tends to 

 favor the formation of the valves of the young embryos. At 4 p, m. to-day 

 another lot were placed in the second McDonald apparatus. At 4 p. m. 

 the next day shells begin to be developed, but are not so far advanced 

 in this respect as the first lot in the first closed circuit apparatus, and 

 it must also be borne in mind that the temperature of the water is now 

 rising. Temperature of the water to-day has ranged from 79° to 88° Fahr. 



July 25. — The lot of embryos which were fertilized on the 22d are 

 still developing finely, and we find that the continuous current of water 

 passing through the jars taken from the closed circuit yesterday does 

 not detach the affixed fry, as revealed by microscopic examination. 

 Allowing a stream of water to pour over the shells to which the fry 

 has attached itself, does not detach the latter, nor does a lively move- 

 ment through the water of shells, to the surface of which fry has at- 

 tached itself, produce any detachment of the latter. The entire animal 

 is now covered by the valves; the velum is, however, still protruded. 

 The protrusion and retraction of the velum is evidently effected by the 

 relaxation and contraction of the minute pallial muscles of the embryo. 

 The fixation of the first lot of the 22d must have taken place about 

 twenty hours after the ova were fertilized and began to develop. Strangely 

 enough the embryos fertilized yesterday at 4 p. m. as yet show no signs 

 of having attached themselves to the inside of the jars and aquaria 

 comprising apparatus No. 2. The temperature of the water in the ap- 

 paratus to-day ranged from 80° to 84° Fahr. 



In order to study the fry which was put into the McDonald appa- 

 ratus No. 1 on the 22d more narrowly, we removed some of the shells 

 from the bottom of one of the hatching jars and scraped the surface 

 with a sharp scalpel. Examining the sediment removed in this way, 

 under high powers of the microscope, we very readily discovered some 



