June 19, 1908] 



SCIENCE 



949 



stained in Delafield's hematoxylin there is 

 every indication that the attachment is 

 through the intermediary of these cells. 

 However, in thin sections (2 fi-3 /j.) fixed 

 in Flemming's fluid and stained in iron 

 hematoxylin it is seen that the muscle 

 fibrilliE pass through the cells and thus 

 attach directly to the cuticle. Study of 

 developing muscle indicates that, in Sneth- 

 lage reports for Artemia, the cells are epi- 

 thelial muscle cells which give rise to the 

 chitin, on the one hand, and to the muscle 

 as well. 



The Skeletal Parts of the Sand-dollar: 

 Emily Rat Gregoey, Wells College. 

 The test of the sand-dollar follows the 

 structure typical for echinoderms, but has 

 some interesting modifications. The ap- 

 ical region is occupied by a single plate 

 which functions as the madreporite. The 

 minute pores are irregularly arranged and 

 increase in number as the animal grows. 

 There are genital pores at the junction of 

 the central plate and the first pairs of in- 

 terradials 1-4, but the pore is wanting in 

 the interradial area 5. Ocular pores occur 

 between the central plate and the first pairs 

 of ambulacral plates. The anus is found 

 on the ambitus between the rows of inter- 

 radial area 5. Oral plates are wanting and 

 there are only minute calcareous granules 

 in the membranous peristome. The ring 

 of plates nearest the mouth consists of ten 

 (paired) ambulacral plates, and five, there- 

 fore unpaired, interambulacrals. Some 

 authors appear to refer to this now as the 

 peristome. The coronal portion of the test 

 with its peculiar petal areas is familiar. 

 The line of the ambitus does not correspond 

 to the sutures between the plates. The 

 perignathic girdle is reduced to an incon- 

 spicuous ridge, but on the unpaired inter- 

 radials there are wedge-shaped apophyses 

 to support the lantern. The number of 

 plates on the oral surface is established by 



the time the test is 7 mm. in diameter ; after 

 this these plates increase in size but not in 

 number. The number of plates on the 

 aboral surface increases until the diameter 

 of the test is 46 mm. After that a few 

 more plates may be added to the petal area 

 as the last interambulacrals increase in 

 size. Increase in the number of plates 

 occurs only at the edge of the central plate 

 and is, of course, greatest in the ambulacral 

 area. There may be seven or even nine 

 plates in the petal to one interradial. All 

 the plates of the ambulacral system are 

 primary; no such secondary and tertiary 

 plates are found here as are seen in 

 Echinus (Chadwick). The pores in the 

 petal area are all between the plates. Else- 

 where they may pass through the plates. 

 The unpaired pores increase in number 

 from the petal to the edge in wedge-shaped 

 areas which meet, and there is a dense ring 

 of them about the ambitus where there may 

 be three or four rows of pores through a 

 single plate. 



The inner surface of the skeleton shows 

 remarkable structures. The distal half or 

 third is almost covered with pillars smd 

 ridges which grow from both surfaces and 

 fuse, leaving small irregular spaces be- 

 tween. The spines in cross-section are 

 star-shaped, with four to thirteen points. 

 Longitudinally they show a fenestrated 

 structure. Six forms are to be distin- 

 guished in different areas. 



A Study of Colorado Entomostraca: Gid- 

 eon S. DoDDS, University of Colorado. 

 Up to 1902 but 10 species of Entomos- 

 traca were listed from Colorado. That 

 year Beardsley published a list which in- 

 cluded 24 species new to the state. His 

 collections were from the plains region. In 

 1904 Professor Henry B. "Ward added 8 

 species from alpine lakes in the Pikes Peak 

 region, and in 1907 Chaneey Juday listed 

 10 more from Twin Lakes. Three others 



