778 PROFESSOR J. STEPHENSON ON 



epithelium and gonocoel wall, would presumably at first give rise to a number of 

 vacuole-like spaces ; later, these would spread and fuse here and there to form a 

 network ; while in some cases the process might go further still, and result in the 

 formation of a peri-intestinal sinus. My own idea of the formation of a sinus, in 

 those cases where it occurs, corresponds to the description by Gamble and Ashworth 

 (20) (also referred to by Lang, p. 210), who show that the intestinal sinus in the 

 Arenicolidjie is a secondary formation ; the original condition ontogenetically is that of 

 a plexus, which later gradually extends itself by the fusion of the individual vessels to 

 form a continuous sinus. I cannot help thinking that Lang has added to the difficulties 

 of the theory by assuming a continuous sinus as the original condition, from which, in 

 most cases, a network has been formed by subsequent approximation and adhesion 

 of the tissues of the coelomic wall to the alimentary epithelium. 



The evidence, I think, is the other way. Firstly, as stated above, it seems on 

 mechanical grounds easier to conceive the network as giving place to the sinus than 

 vice vei'sd. Secondly, the network is the commoner, the sinus the rarer condition ; 

 and, indeed, this is probably the case in greater degree than at first sight appears, since 

 what is really a network has frequently been called a sinus.* And thirdly, as mentioned 

 above, in the Arenicolidae a plexus does actually give place to a sinus during individual 

 development. 



(2) (Thesis 9). — The contractility of the vascular walls is supposed by Lang to be 

 derived from the contractility of the walls of the gonadial sacs, which came into play 

 primarily for the purpose of expulsion of the genital products ; these contractions 



* We may take, for example, the case of the Eiichytrseidae (cf. Lang, op. cit., pp. 210-216). The perienteric "sinus" 

 here, according to Michaelsen (quoted by Lang), is " eher ein dichtes Netz von Blutkanalen," or, according to another 

 paper of the same author, " besteht aus vielen hart nebeneinander verlaufenden Kanjilen." So, too, I have observed in 

 a specimen of Lx(,mhricillus sahterraneus, in which the posterior part of the body was much engorged and the blood 

 coagulating, that the ajjpearance in the alimentary wall was that of a thick, close-set network of large vessels, v.'itli 

 hardly any interspaces between them. 



Beddard, discussing this point (quoted by Lang, p. 215), also speaks of a network, and doubts the existence of a 

 continuous sinus. Lang here takes Beddard to task, remarking, " Sodann bezweifelt Beddard auch, man weiss nicht 

 weshalb, die Eichtigkeit der verschiedenen Angaben von Michaelsen und Vejdovsky iiber den Darniblutsinus der 

 Encliytriiiden." Lang is, however, wrong, at any rate as regards Beddard's attitude towards Michaelsen. Michaelsen 

 speaks of " a close network of blood-channels," and of " numerous closely approximated channels." Though STich a 

 condition may perhaps loosely be called a "sinus," it is certainly more properly described as a network ; Beddard, 

 using the words in their strict significance, is in agreement with Michaelsen's facts, though possibly differing in the 

 name he uses to denote the condition. 



As illustrating the loose use of the term " sinus " referred to in the text, I may take two instances, quoted by Lang 

 though with a different object. On p. 214 Hesse is apparently made to speak of " Darmsinuskanale," and " Darmsinus- 

 kapillaren" ; and Lang himself a few lines lower speaks of "die Kanale des Blutsinus" ; such expressions are, to my 

 thinking, self-contradictory, since, if a system consists of canals or capillaries, it cannot at the same time be a continuous 

 space, — which is what I take the word " sinus " to mean, and which is the sense required by Lang throughout his 

 discussion of the origin of the vascular system. Again (top of p. 217), Hesse speaks first of a "blood-sinus," then of 

 cells whose long diameter coincides with the axis of the "blood-vessel" (des Blutgefasses), and lastly of a "blood-sinus" 

 again. I may add that Vejdovsky apparently uses the expressions "sinus "and "network" without distinction ; thus 

 (.55, p. 155, 156), "sog. Darniblutsinus" and " sog. Blutsinus," of Oligochteta in general ; (p. 85) of Pherelima, "des 

 sog. Blutgefjissnetzes (Darniblutsinus) " ; (p. 119) " Darmsinus" and " Darniblutsinus," of Pheretima ; (pp. 125 and 139) 

 " Darniblutsinus," of Dendrohaena, a Lumbricid ; it would seem that he holds the view that the system is essentially a 

 sinus throughout the Oligochseta : — "Der Darniblutsinus (of Pheretima) gestaltet sich von der Oberfliiche als das 

 sog. Darmgefiissnetz, indem er in einzelne langs- und ringsverlaufende Kanale abgeteilt ist, die untereinander kom- 

 munizieren. An Querschnitten erscheint er als eine machtige Lakune , . . " (p. 119). 



