242 SUMMARY OF CURRENT RESEARCHES RELATING TO 



This differs from Stenothoe Dana in having the ramus of the last pair 

 of pleopods uniarticulate ; in most of its characters it approaches 

 Allorcliestes, being distinguished from it only by the largely developed 

 anterior coxse and the character of the telson. 



Circulatory Organs of Isopoda.* — M. Delaze states that the heart 

 of these Crustacea is situated in the abdomen, and extends more or 

 less into the thorax. It is altogether dorsal in position, tubular when 

 long, pyriform when short. It communicates with the pericardium 

 by two or four orifices, which close when the heart contracts. When 

 the heart does contract, it not only dimiuishes in volume, but produces 

 a kind of vacuum, and so a kind of asjjiration, which attracts fresh 

 quantities of blood to the pericardium. Eleven arteries — one thoracic, 

 two abdominal, six thoracic, and two lateral — are given off from the 

 heart. These arteries have bilabiate valves at their orifices. After 

 describing the course taken by these vessels to the various organs 

 which they supply, the author points out that there is developed a 

 peri-CBSophageal vascular collar, placed above the (^esophageal com- 

 missures. From this collar there is given off a pre-neural artery, 

 which passes to the anus along the anterior median line of the body, 

 above the ganglionic nervous chain. The ventral arterial system is 

 formed by seven pairs of branches derived from the thoracic arteries, 

 and by others given off from the pre-neural artery. These unite by 

 anastc moses, and in some cases give rise to a superficial vascular 

 circle. There are no capillaries, the arterioles passing the blood into 

 interstitial lacunse, the largest of which is found in the thorax. 



At the base of the thorax the two chief thoracic sinuses unite, and 

 give rise to a large abdominal sinus, which is situated in front of the 

 rectum. From this sinus five pairs of vessels pass off to the gills. 



It ordinarily happens that certain parts of the abdomen, such as the 

 telson, or the epimera of the branchiferous somites, are adapted for the 

 purposes of respiration. Five pairs of branchio-pericardiac vessels, 

 formed by the efferent branchial canal, pass backwards, and open into 

 the pericardium by non-valvate orifices. 



The pericardium surrounds the whole of the heart, except in front, 

 where it is united to the rectum. It is generally formed by a distinct 

 membrane, and its walls appear to be invested by a layer of endo- 

 thelium. With the exception of the first-mentioned orifices, it is 

 closed, except on its superior surface, where there are some small 

 lacunae. A small number of globules which have not undergone the 

 respiratory process enter by these clefts, and mix with the blood 

 which has come from the branchise. Some of these have returned from 

 the thoracic lacuna by means of the dorsal arcs, which are placed 

 just below the integument. 



New Type of Parasitic Crustacean. j — M. Lacaze-Duthiers de- 

 scribes a new parasitic Cirriped (Laura), which he has found living on 

 that Antipatharian form to which he has already given the generic 

 name of Gerardia. Seen from without, it is reniform in shape and its 



* Compfes Reijlus, xcii. (ISSl) pp. G3-6. 



t Arch. Zool. Expe'r. et Glen., viii. (ISSO) pp. 537-81. 



I 



