22 PHLEBCEDESIS AND HsEMOCCEL 



due to English morphologists, the later developments of our know- 

 ledge as to what is and what is not " coelom " are very largely due 

 to the same school. 



In 1881 I undertook an investigation of the blood-systems of 

 both Mollusca and Arlhropoda, at that time held by me and by 

 nearly all other morphologists to represent coolom, either in con- 

 sequence of the confluence of two systems at one time separated, 

 or by survival of an undifferentiated condition. 



At that time the pericardium of the Lamellibranchia in par- 

 ticular, and of all other Mollusca by implication, was held to be a 

 blood space in communication by veins with the general blood- 

 system. In Anodon the apertures of these veins were pointed out 

 in text-books of Comparative Anatomy on the anterior wall of the 

 pericardium. I found that the fluid in the pericardium of Anodon 

 is not blood, and that the so-called apertures of veins on its wall 

 are the apertures of a remarkable branching tubular system (form- 

 ing, in large part, the organ of Keber, but extending far beyond 

 it). I found, further, that in Gastropoda the pericardium does 

 not contain blood. The red-blooded Lamellibranch, Solen (Cerati- 

 solen) legumen, which has oval corpuscles coloured by haemoglobin 

 in its blood, appeared to me likely to furnish a valuable case for the 

 study of this question. One of my pupils, Mr. Penrose (British 

 Association Reports, 1882), and subsequently I myself (Zoologischer 

 Anzeiger, 1884), examined Solen legumen in the living condition, 

 and also by means of sections, and established the fact that the 

 red blood never enters the pericardial chamber, and, further, 

 that no blood is exuded from the animal's body (by pores or 

 otherwise) when it rapidly retracts the foot after previous 

 expansion. Other investigations which I had commenced in 1867 

 on the renal organs of Patella were resumed, and led me to the 

 conclusion that the pericardial space of Mollusca is not a blood 

 space, and that it is in communication with the renal sacs by 

 ciliated reno - pericardial apertures (often funnels) which lead 

 through the renal sacs (" urocoels," according to our present 

 nomenclature) to the exterior. I thus came to the conclusion that 

 the pericardial chamber (and its Keberian tubules in some Lamelli- 

 branchs), together with the gonad sacs, which in Neomenia and 

 Cephalopoda communicate with the former, are the real ccelom of 

 Mollusca. At first I adhered to the dominant theory that the 

 blood-holding space is also to be regarded as a part of the coelom 

 but shut off from it. But a subsequent consideration of the blood- 

 system of the Arthropoda, and of the fact that the more primitive 

 Mollusca (the Polyplacophora and the Cephalopoda) have well- 

 developed tubular blood-vessels largely developed, led me to put 

 forward the theory of Phlebcedesis. According to this theory, 

 the true coelom is present in a reduced form in both Mollusca and 



