468 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 31 



V. MOUTH PARTS OF A CRUSTACEAN 



It was recommended in the introductory section of this paper 

 that entomologists should not confine their investigations to insects, 

 since valuable information bearing on the structural evolution of 

 insects may often be obtained from members of related groups of 

 animals. Specialization is a necessity, but it should not be carried to 

 the extent it is practised in some institutions, where it is regarded as 

 a breach of professional etiquette for a specialist in one group to 

 acquire any first-hand information in the field of another specialist. 



In sleuthing out information by the method of examining the rela- 

 tives of an animal under investigation it is always important to be 

 able to pick out a communicative subject. On the island of Tasmania 

 there live two little fresh-water crustaceans, named Anaspides and 

 Paranaspides. An interesting account of the life and habits of these 

 two isolated creatures is given by Miss S. M. Manton (1930). 

 Paranaspides inhabits the Great Lake of Tasmania situated at a 

 height of 3,700 feet. Anaspides lives on Mount Wellington in 

 streams and pools provided with running water, mostly above 1,400 

 feet and up to an altitude of 3,600 feet. The general appearance 

 and attitudes of these crustaceans, as shown in Miss Manton's col- 

 ored plates, are very much like those of such apterygote insects 

 as Machilis and its relatives; but we must be cautious of assuming 

 an}' close relationship between insects and crustaceans, though their 

 appearance and even their structure may be in some cases strikingly 

 parallel. However, Anaspides and Paranaspides are relatively prim- 

 itive members of the group of crustaceans (Malacostraca) that in- 

 cludes the shrimps, crayfish, and crabs, and a study of their mouth 

 parts will give a very plausible suggestion of how some of the 

 structural features of insect mouth parts may have been evolved from 

 ordinary leg structures. The feeding habits of Anaspides and its 

 relatives, described by Cannon and Manton (1929), are of course 

 different from those of any insect, but functional differences do not 

 often obscure fundamental structural similarities. 



Through the interest of Dr. Waldo L, Schmitt, of the United 

 States National Museum, the writer has been able to make a personal 

 study of specimens of Anaspides tasinaniae (fig. 16). As already 

 shown in the description of the head, the large mandibular segment 

 of Anaspides {B, IV) is followed by a composite segment {V+ 

 VI+VII) bearing two pairs of maxillae (i Mx, 2 Mx) and the first 

 pair of maxillipeds {1 Mxp). The maxillipeds are typical, leglike 

 appendages, each composed of seven segments (fig. 17 A). The 

 first segment is the basis (LB), usually called the coxopodite {Cxpd) 

 by students of Crustacea. The next three segments are the first 



