BULLETIN OF THE UNITED STATES FISH COMMISSION. 239 



Brady (Mouograph British Copepoda) observes in liis introductiou, 

 vol. i, page 9: "The beds of fresh- water lakes seem to be very sparsely 

 populated with Copei)oda, aud as to swimmiug species it may, as a 

 general rule, be said that the weedier the pool and the smaller its ex- 

 tent, the more abundant in all ])robability the Entomostraca. 



" Many of the marine species pass their life apparently near the sur- 

 face of the open sea, and some of these, such as Calanus finmarchianusy 

 Gunner, aud Aiiomolocera Patersonii, Templeton, are frequently found 

 in immense profusion, the first-named species having been said to form 

 a very important part of the food of the Greenland whale, and it is re- 

 markable that in the Arctic seas not only do the Entomostraca attain 

 an enormous development in point of numbers, but also in individual 

 size; Arctic specimens, for example, of Calanus fiinmarcliianus aud Me- 

 iridia armata being many times the bulk of those taken in our own lati- 

 tude." {I.e.) 



According to H. Woodward, in his article Crustacea, Encyclopaedia 

 Britannica, the fecuudity of the Copepoda is truly surprising. " Cyclops 

 quadricornis is often found with thirty or forty eggs on each side, and 

 though those species which have but a single ovisac do not carry so 

 many, their number is still very considerable. Jurine isolated speci- 

 mens of Cyclops, aud found them to lay eight or ten times within three 

 months, each time about forty eggs. At the end of a year one female 

 would have produced 4,442,189,120 young ! Cetochilus is so abundant, 

 both in the northern seas and in the South Atlantic, so as to serve for 

 food to such an immense animal as the whale. They color the sea for 

 many miles in extent, and when the experienced whaler sees this ruddy, 

 hue upon the ocean he knows he has arrived at the 'pasture of the 

 whales'. They are to be seen in vast quantities oft" the Isle of May in 

 the Firth of Forth during the summer months. Many Cetacea are at- 

 tracted thither, and vast shoals of fish also come to feed upon them. 

 One anomalous type of free copepod is the ISotodelphys ascidicola, de- 

 scribed by Allman, which is found swimming freely in the branchial 

 sack of Ascidia communis.'''' 



The writer, in passing, would remark that he has frequently met with 

 Copepoda swimming freely in the ventral part of the branchial space 

 of il/j/ft arenaria, in which the animals were probably not parasitical or 

 commensal, but had been drawn from without into the respiratory space 

 of the mollusk through the incurrent part of its siphon. 



In the same article as previously quoted Woodward observes: "The 

 Cladocera are chiefly fresh water, and are distributed over the whole 

 world. Of this order the Daphnia pulex, so abundant in our [British] 

 fresh waters, is a good example. So numerous are they in our jjonds in 

 summer as frequently to impart a blood-red hue to the water for many 

 yards in extent. In order to realize the wonderful fecundity of this and 

 allied genera, it is necessary to realize that when a Daphnia is only ten 

 days old eggs commence to be formed within the carapace, and under 



