168 Miscellaneous!. 



Squilla empiisa lives in hard muddy bottom, in or on the sides of 

 channels where there is a rapid current, and it constructs a shallow 

 U-shaped burrow, open at Jboth ends. The burrow is excavated by 

 the current of water produced by the abdominal appendages, and I 

 have never seen them carrying sand out of the holes. They do not 

 arch over the opening, and they are often found swimming at a dis- 

 tance of many feet from the hole, probably in pursuit of prey. 



Squilla stridulates by rubbing the serrated spine of the swimmeret 

 across the serrated ridge on the ventral surface of the telson. The 

 noise which is thus made under water can l)e clearly heard above the 

 surface. — Johns Hopl-ins University Circular, Oct. 1885, p. 10. 



On tJie Heart of the Gamasidse and its Significance in the Phylo- 

 genetie Consideration of the Acarida and Arachnoidea, and the 

 Classification of the Arthropoda. By Prof. Carl Glaus. 



The heart, discovered by M. Willibald AVinkler, which has hitherto 

 remained entirely unknown in the group Acarida, occurs in the 

 posterior region of the body and above the rectum ; it pulsates 

 strongly and rapidly. It is remarkablj' like the heart of the Daph- 

 nidai, and like this is reduced to a single chamber, which is perfo- 

 rated on each side by a fissure furnished with lip-like valves and 

 passes anteriorly into an elongated median aorta. The position 

 towards the posterior end of the body, which is rather surprising at 

 the first glance, is explained by the simplification which the abdo- 

 men of the mite has undei-gone, appearing as a comparatively short 

 unsegmented region, united without any demarcation with the 

 cephalothorax. Hitherto the heart has been demonstrated only in 

 Gamasus, and it is probable tliat its occurrence may be confined to 

 only a few families of the Acarida, perhaps to the Gamasidae alone. 

 It is best seen in all its parts in the six-legged larvse (probably of 

 Garnasvs fucoruni, De G.), in which the integument is comparatively 

 thin. These have probably never previously been examined in the 

 living state under a high power, or the presence of the quickly pul- 

 sating heart coidd not easily have escaped observation. But even 

 through the less transparent skin of the adult animal the heart is 

 not difficult to recognize when one has seen it in the more delicate 

 larva. 



In the unilocular heart of Gamasus we have evidently to do with 

 a retrograde organ. Just as Clans regarded the similar heart in 

 the Cladocera as a secondary simplified form derived from the many- 

 chambered heart of the Phyllopoda, this simple heart in the Mites, 

 with its single pair of fissures, may be regarded as an abbreviated 

 and rudimentary spider's heart, the latter being of elongated tubular 

 form, with three pairs of fissures, and connected with a complex 

 system of arterial vessels. And just as, among the Entomostraca, 

 the unilocular heart of the Ostracoda and Copepoda occurs only in 

 particular families of those orders and is altogether wanting in 

 the lower groups, so in the Acarida the lower families, such as the 



