DESCRIPTIONS OF GENERA AND SPECIES 361 



caeca occur in the not nearly allied genus Urobenus (a Geoscolicid) ; with thia 

 exception they are limited to the present family; in a few species, all natives of 

 Japan, the two caeca are replaced by six or seven, as was first pointed out by 

 HoBST (9) ; but in these cases there is always one pair which are very much larger 

 than the others. A gizzard is, so far as we at present know, invariably found in 

 this family; its position varies. In the genus Megascolex and in Biporochaeta it is 

 placed far forwards — ^in the fifth, sixth, or in the seventh and eighth segments ; 

 in the geiius Perichaeta the gizzard appears with rare exceptions to occupy two 

 segments — the eighth and the ninth. It is often stated to occupy three segments ; 

 and from one point of view it often does; for the septum which bounds the 

 ninth and tenth segments is pushed so far backwards by the growth of the 

 gizzard that the setae belonging to this (the tenth) segment lie to the forward side 

 of the septum that intervenes between the ninth and tenth segments. In this 

 genus (Perichaeta) it is nearly always the case that the septum dividing segments 

 viii/ix is absent. 



It is a doubtful point whether true calciferous glands occur in the majority of 

 Perichaetidae ; in the genus Perichaeta they certainly do not ; they are represented 

 simply by an increased vascularity of the oesophagus in certain segments ; in Biporo- 

 chaeta, however, there are two pairs of calciferous glands in x,' xi ; these are, however, 

 not such distinct caeca of the gut as the same structures are in Pontoscolex ; they 

 present the appearance of local thickenings of the walls of the oesophagus ^ ; the 

 same state of affairs appears to characterise the genus Megascolex according to 

 Fletcher. In Biporochaeta crystals occur in the calciferous glands similar to those 

 which are found in the calciferous glands of other earthworms. Unique in the 

 family is M. coeruleus for the series of intestinal glands, which, however, are again 

 met with in Typhaeus. These are placed upon the dorsal surface of the intestine in 

 segments xxi-xxxix (about). Their lumen is lined by a much-'folded cellular membrane ; 

 their structure in fact is not unlike that of the calciferous glands. 



A typhlosole has been stated to be wanting in the Perichaetidae ; it is as a 

 rule present, but never appears to attain to such dimensions as it does, for example, 

 in the Acanthodrilidae. 



With regard to the vascular systeTn, a subnervian vessel, sometimes stated to be 

 absent, is present at any rate in some forms. The details of the circulatory system, 

 at present only known in M. coeruleus, will be gone into below. The last pair of 

 hearts is usually ia segment xii or xiii. 



' Besidesj this genus is possibly not referable to this family, but rather to the Acanthodrilidae 

 (see below). 



3A 



