ECONOMIC RELATIONS, ANATOMY, AND LIFE HISTORY OF GENUS LERN^A. 19I 



SYSTEMATIC. 



The genus Lemma differs from the other Lernaean genera in the following 

 particulars : 



1. The body is formed by a lengthening of all the thoracic segments instead of only 

 the fifth and sixth. This separates the swimming legs and leaves them distributed 

 throughout the length of the body instead of being bunched closely together behind 

 the head; moreover there are five pairs of legs instead of four or only three. 



2. The first antennse are on the anterior margin and the second antennae are on 

 the ventral surface of the head, instead of being dorsal, and while the second pair are 

 uncinate they are not chelate. There are two pairs of maxillae and a pair of well- 

 developed maxillipeds, instead of a single pair of maxillae. 



3. The egg strings are relatively short and club-shaped or spindle-shaped instead of 

 being long and filiform. The eggs are large and spherical and multiseriate instead of 

 being flattened into thin disks arranged in a single series like a row of coins. 



4. In the ovary egg filaments are formed, consisting of oocytes packed tightly 

 together in a single row; these separate from one another at the entrance into the 

 oviduct and each oocyte absorbs food and yolk and becomes an egg. In the oviducts 

 the eggs remain spherical and are arranged loosely in one or two rows. In the other 

 Lemseidse there are no egg filaments, but the eggs are formed singly and are tightly 

 packed together in a single row exactly like those in the external cases. 



5. The copepodid larvae have no frontal filament but attach themselves to their 

 first or temporary host by means of the second antennae and the maxillipeds. Hence 

 there is no loss nor even any diminution of the power of locomotion during the 

 copepodid stages. In the other Lemaeidae there is a large frontal filament, and while 

 the larva is attached by it to its temporary host the swimming legs and some of the 

 mouth parts degenerate and become immovable, but are restored to their former con- 

 dition during the second free-swimming period. 



It would seem at first as if these differences were enough to separate this genus 

 from the other Lemaeids and to make of it a distinct family, as was advocated by 

 Briihl. But as we examine and compare more closely we find similar differences among 

 the other genera, which naturally lead up to the ones here mentioned. 



In other words, these are differences in degree rather than in kind, and hence 

 would not warrant separation as a distinct family. Thus in Penicidus there is an 

 elongation of all the thorax segments, with a consequent separation of the swimming 

 legs, and what we find here is only the same thing carried a little further. Again, most 

 of the Lernaean genera have four pairs of swimming legs, but there are some that have 

 three pairs and others that have only two, so that there is no fixed and constant 

 number, and the presence of five pairs only makes the series so much the more complete. 



The copepodid larvae of such genera as are known possess the same antennae and 

 mouth parts as those of the present genus. It is only in the subsequent metamor- 

 phosis of the female that some of them are lost, and it is evident that such a loss by one 

 sex only could hardly constitute a family distinction. The differences in the external 

 egg strings and in the internal ovary and oviducts are very real differences, but even 

 in this particular the other genera are not alike. In some the egg tubes are coiled 

 into a tight spiral, in others they are gathered into a loose mass, while in most of the 

 genera they are straight, filiform, and much longer than the entire body. The lack of 

 a frontal filament is duplicated among the Caligidae, where the larvae of the Caliginae, 



