CRUSTACEANS 



the sides of the glass vessel in which the mother was kept. This method, reminiscent of 

 molluscan habits, is strikingly different from that of Copepoda, which normally carry the 

 extruded eggs in ovisacs attached to their own bodies. Cuvier described also the four pairs of 

 two-branched feet as serving both for locomotion and respiration, being perpetually in move- 

 ment, whether the animal were swimming or at rest. One of the remarkable peculiarities of 

 this species, but not common to the whole family of the Argulidas, is the transformation of 

 one pair of maxillz into suckers. These give the animal secure adhesion to the fishes, from 

 which by other organs it derives a bountiful meal. When sufficiently gorged it can loose 

 hold and disport itself freely in the water. There is no narrow exclusiveness in its attach- 

 ments, for it has been observed on carp and roach, pike and perch, trout and salmon-trout, 

 as well as on the humble stickle-back and the tadpole of the frog. The bream is an addition 

 to the victims on which this sanguinary persecutor battens for the nutriment of its little flat, 

 greenish, roundabout body. 



The Cladocera, which owe their name to their two-branched second antennas, unlike the 

 Argulidae, are a much diversified order of the Branchiopoda. In place of the two separate 

 compound eyes and median eye-spot which our Argulus enjoys, they have but one eye, with 

 or without an eye-spot in attendance. They have a more or less distinct head, and the rest of 

 the body in general covered by a bivalved sheath. They have from four to six pairs of feet. 

 They share with many other Entomostraca a privilege highly conducive to the preservation 

 and distribution of the race. While essentially aquatic animals that cannot live without 

 water, they can, nevertheless, sow the seed of future generations in defiance of drought. 

 For example, in January of this present year I conveyed from one county to another a little 

 earth scooped up from a piece of grassland which was not then, but sometimes is, covered by 

 a thin stratum of water. Some ordinary drinking water was poured upon this dried mud. 

 For some weeks it showed no sign of crustacean life, but at length on the agth of the month 

 I noticed some moving specks, and on the following 4th of February I was able to take out and 

 dissect a full-grown Daphnia pulex laden with thirty-five well-advanced eggs. Of this vivacious 

 and abundant order Mr. Pratt's list mentions ' Daphnia pulex. Ponds and ditches in many 

 places about Nottingham. D. schiefferi. Pond at Gamston, near Nottingham. D. reticulata. 

 Ponds about Nottingham. D. vetula. Ditch near Beeston. Chydorus sphfericus. Ditch near 

 Beeston. Eurycercus lamellatus. Old pond at Strelley.' In Mr. Edwin Smith's lecture various 

 species are mentioned with some account of their peculiarities, but no statement that they had 

 been observed in Nottinghamshire, although a species of Macrothrix is noted as having been 

 found elsewhere. This notice is succeeded by the following paragraph : ' One other family 

 of the Cladocera should be mentioned, if only because it contains Chydorus sphaericus, a very 

 common species in our stagnant ponds. The .Lynceidae (for so the family is called) may be 

 recognized by a black spot situated in front of the eye, and looking not much unlike a second 

 eye, which, however, it is not. The intestine, moreover, makes one complete turn and a half. 

 To the same family belong Eurycercus lamellatus and Acroperus harpce, both of which occur in 

 this neighbourhood. The latter is fond of resting on the top of the water, moored by its 

 antennae to a bit of weed, or a cluster of them will collect round some floating leaf or sprig, 

 and lie motionless in the warm sunshine as if asleep.' From references in other parts of the 

 essay it is clear that the expression ' this neighbourhood ' relates to Nottingham. 



There is no reason whatever for doubting that the species recorded in the above quoted 

 lists occur in this county. It would rather be a marvel if they did not. But some comment 

 may be offered on their names and distinctive characters. In the family Daphniidae the second 

 antennae have the dorsal branch four-jointed, the ventral one three-jointed ; of the five pairs 

 of feet, the last is remote from the others, and the intestine is not convoluted. The typical 

 species, Daphnia pulex (de Geer), is extremely common. It is also very mutable, so that a 

 medley of specific, subspecific, and varietal names has grown round it. D. schtefferi (Baird) is 

 now identified with the earlier D, magna (Straus), and earns its specific name by attaining a 

 much more considerable size than its commoner relation, the female becoming about a sixth of 

 an inch long as contrasted with a tenth of an inch measured by the other species, in each case 

 the terminal spur not included. 1 The D. reticulata of Baird is now known as Ceriodaphnia 

 reticulata (Jurine), the genus being distinguished from Daphnia by having the first antennae of 

 the female movable, and by the hexagonal or pentagonal pattern of the reticulation on its 

 shell. It must, however, be understood that the name as used by Baird is considered now to 

 cover not only three varieties of Jurine's species, but two other species in addition, namely, 



1 Brady, in Nat. Hist. Trans. Northumberland, etc., vol. xiii, pt. ii, pp. 222, 242 (1898). 



149 



