THE ANATOMY. COELOM 27 



worms one would be disposed to put down the immense numbers of free corpuscles 

 to the process of asexual reproduction with which their presence seems to be con- 

 nected. But this will obviously not do for the Enchytraeidae, where there is of 

 course no asexual reproduction^. Among earthworms there is generally not such 

 a great abundance of corpuscles ; but in many Eudrilids there is — a circumstance 

 which gives to these species in many cases a milky white appearance (e. g. Megachaeta 

 alba). In the embryos of Octochaetus I noticed a very large quantity of corpuscles, 

 the presence of which may be related to rapid growth and excretion. There are in 

 most, if not all, Oligochaeta apparently the equivalents of phagocytes ; these were 

 first noticed by Hoffmeisteb. Generally in the posterior region of the body are to 

 be seen masses of brownish cells enclosing old and broken setae ; the latter are 

 evidently in the process of removal by disintegration; possibly this goes on until 

 they can be thrown out of the body by the dorsal pores or the nephridia. 



§ I. Perihaemal spaces. Besides these chambers, formed by a sub-division of the 

 cqelom, there exist others which for the most part involve various portions of the vas- 

 cular system. The first structure of the kind to be described occurs in the Acanthodrilid 

 Deinodrilus ; in this worm the dorsal vessel is seen on a dissection to present an 

 obscured appearance, which is due to the fact that it is enclosed in a sac which 

 completely surrounds it and separates it from the general body-cavity. In this worm 

 the dorsal vessel is completely double, and corresponding to this is a separation between 

 the two halves of the ' pericardium.' In transverse sections, through the dorsal vessel, 

 the sac in which each of the two trunks lies, is seen to consist of a very delicate 

 muscular layer, which is covered externally and lined internally by a cellular coat ; 

 the external covering is formed of few and dehcate cells ; on the other hand, the 

 internal lining consists of large cells, which are here and there heaped up into piles. 

 At intervals delicate strands of muscular fibres pass from the walls of the sac to 

 the contained blood-vessel, where they pass between the large chloragogen-cells which 

 cover the blood-vessel and become lost in. its muscular layer. This perihaemal space 

 seems to commence a little way behind the head of the worm, but I have not fixed 

 the actual point at which it commences, nor its connexion, if any, with the general 

 coelomic space. 



Spenceb (1) subsequently recorded the presence in Megascolides of a similar sac 

 enveloping the dorsal vessel ; in this case, however, there is a further compKcation. 

 It possesses in fact a series of diverticula, one more dorsal, the other more ventral 

 in position ; these- diverticula — the dorsal ones especially as figured by Spencer, 

 are crammed with free and slightly attached cells ; the main tube enveloping the 



' Cf. however Lemoine (2), by whom simple division is stated to occur. 



E 2 



