ENTOMOSTRACA. 



29 



the degradation of form is still further carried. These misshapen, distorted creatures 

 resemble nothing but the imcanny figures of a nightmare. Small as they are, they 

 arouse in the spectator an involuntary feeling of disgust that 

 such abortions should be found in the group of animals. By 

 what law of nature it follows that parasittes should pay for their 

 habits by their loss of beauty and symmetry of form, it is per- 

 haps hard to say, but the fact is undoubted. Wholly apart 

 from a knowledge of their habits, these and most other para^ 

 sitio forms of animals awaken feelings of disgust. Very few 

 are even neutral aesthetically ; fewer still are eyen moderately 

 beautiful, and those are of the less truly parasitic forms. 



In many of these j)arasitic Crustacea the males are much 

 smaller than the females, — so-called pigmy-males, — and are far 

 less numerous. The females, as is the case in most parasites, 

 produces enormous numbers of eggs. 



The development for a time is essentially similar to that 

 of the preceding order. The eggs are carried in egg-pouches 

 (shown in the figures of Dinematoura, Pandarus, Hbemobaphes, 

 and IiemcBonema), and from them hatch true nauplii. After 

 hatching, the young pursues a type of development peculiar to 

 the family to which it belongs ; but in all cases it is the female 

 which undergoes the most extensive metamorphosis, the males 

 diverging but little from the normal crustacean type. 



Oeder. in. — ostracoda. 



As in many another group of minute animals, we have to 

 turn to Europe and European forms for a knowledge of the 

 one now before us, for the reason that these forms have been 

 almost entirely neglected by our own observers, who have had 

 larger, but no more interesting, animals to study and describe. 



The Ostracoda are generally very small, and have hard (and 

 frequently calcified) bivalve shells, which often are so opaque 

 that only the most indistinct views can be had of the internal 

 structure without the aid of the somewhat delicate operation 

 of dissection. This bivalve shell is usually ornamented, and 

 by the peculiarity of this ornamentation, as well as the structure 

 of the internal portions, are the species recognized. In the 

 fossil forms the former group of characteristics alone can be 

 used. Some of these markings are produced by the attachments 

 of strong adductor muscles, which pass from one valve to the other, and which by 

 their contraction close the shell. 



The shells of the Ostracoda are usually lenticular or reniform, and frequently one 

 end is a little larger than the other. On removing one of the valves the internal 

 structure can be made out with little difficulty. Only seven pairs of appendages are 

 present ; the two pairs of antennje are large, extending beyond the valves, and with 

 their long fringes of hairs are well adapted for purposes of locomotion, in which they 

 are the principal organs. The mandibles are strong, and the mandibular palps are well 



Fig. 38. — PenellafiU)sa,\ieax- 

 ing a barnacle, Conchoder- 

 ma virgata (see also p. 19). 



