DESCRIPTIONS OF GENERA AND SPECIES 447 



various species which make up these two genera are: (i) the meganephric or plecto- 

 nephric condition; (2) the tubular or lobate character of the spermiducal glands; 

 and (3) the presence or absence of penial setae. 



Only four species, viz. M. tuberculatus, M. illawarrae, 0. mediterreus, and 

 C. rubens, have penial setae. They do not, however, show any other marked 

 characters in common which would justify their separation and inclusion in a distinct 

 genus. Accordingly, I prefer to pass on to the other characters. 



SPENCER (2) does not make use of these particular characters in separating the 

 genera; we find, for example, that ' Megascolides ' contains species with tubular and 

 lobate spermiducal glands ; the same genus also contains species with a plectonephric 

 and with a meganephric excretory system ; on the other hand, all his species of 

 Cryptodrilus have tubular spermiducal glands and paired nephridia, with the sole 

 exception of C. dubius, where there are three pairs of nephridia to each segment 

 possibly hardly to be regarded as an exception, as it has not, at any rate, the truly 

 diffuse nephridia. It will be further noted from the accurate and highly useful details 

 given by SPENCER that in these worms the last pair of hearts are in the twelfth 

 segment. In all the species of worms described by SPENCER in the paper just referred 

 to we find that paired nephridia are associated with the existence of the last pair of hearts 

 in the twelfth segment. Whereas in those species which have a diffuse excretory system 

 the last pair of hearts are in the next, i. e. the thirteenth segment. Moreover, these species 

 which are characterized by the two points referred to, have nearly always lobate spermi- 

 ducal glands ; there are exceptions to this statement, however ; for example, M. australis, 

 M. incertus, M. gippslandicus (? as to its real distinctness from one or other of the 

 above) have a diffuse nephridial system with tubular glands. Out of the twenty-one 

 species of Megascolides and Cryptodrilus, with whose anatomy SPENCER has made 

 us acquainted, sixteen conform to the association of characters just mentioned : they 

 have either (i) paired nephridia, tubular spermiducal glands, last pair of hearts in the 

 twelfth segment ; or (2) diffuse nephridia, lobate glands, last hearts in the thirteenth 

 segment. There are three exceptions to this rule ; these are C. intermed.ius, M. sinuosus ; 

 in the former of the two paired nephridia are associated with tubular glands, but the 

 last pair of hearts are in the thirteenth segment ; in the latter diffuse nephridia are 

 associated with the last pair of hearts in the thirteenth segment, but the spermiducal 

 glands are tubular. 



In the following table the chief structural features of most of the species placed 

 in the above two genera are set forth. 



