56 ORIGINAL ARTICLES. 



laria, it would only be necessary to shorten the oesophagus a little more, 

 and then the wall of the corpus adiposum would be immediately attached 

 to that of the body. So far, therefore, as concerns the corpus adiposum 

 and the oesophagus, Sphaerularia agrees neither with Gordius nor Mer- 

 mis, nor indeed with one more than the other, since, if it agrees with 

 Mermis albicans in the double series of large fat-cells, it has no 

 oesophagus, and in this respect more nearly resembles Gordius. 



Sphaerularia agrees with Gordius in the possession of a terminal vulva, 

 but differs both from that genus and from Mermis in having only a 

 single ovary. As regards the development of the young, Sphaerularia 

 resembles Gordius in undergoing a metamorphosis ; but with this remark- 

 able difference, that whilst the former begins with the filiform or 

 Nematoid condition, the latter ends with it. Mermis, on the other 

 hand, undergoes no metamorphosis ; in all stages of development this 

 worm, like the embryo of Sphaerularia and the adult of Gordius, is fili- 

 form and Nematoid ; so that we may say of the three genera, that the 

 metamorphosis is progressive in Gordius, absent in Mermis, and retro- 

 gressive in Sphaerularia. 



On the whole, it is, I think, evident that Sphaerularia constitutes a 

 group equivalent to Gordius or Mermis, and indeed farther removed 

 from them than they are from one another. Omitting, then, those 

 points as to which, from the imperfection of our knowledge, no conclu- 

 sions are at present attainable, we shall get the following as the prin- 

 cipal characteristics of the three genera: — 



Mermis albicans. — Skin partially covered with papillae. (Esopha- 

 gus long, contained in an outer tube, within the outer membrane of 

 which is a series of nuclei, at sub-equal distances. No intestine or anus. 

 Organs of excretion three in number, and occupying the ventral and 

 lateral lines of the body. Ovary double ; vulva opening at the middle 

 of the body. No metamorphosis, the young being filiform. Males of mo- 

 derate size, free. Spiculae two in number. 



Gordius. — Skin smooth, or in part provided with short spines. 

 (Esophagus very short. Corpus adiposum containing several series of 

 cells. No intestine nor anus. Ovary double ; vulva terminal. Meta- 

 morphosis progressive, the young not being filiform. Males of mode- 

 rate size, free. No spiculae. 



Sphjsrttlaria. — Skin covered with spherules. (Esophagus want- 

 ing. Corpus adiposum consisting of a double series of large cells. No 

 intestine nor anus. Ovary single ; vulva terminal. Metamorphosis re- 

 trogressive, the young being filiform. Males very minute, attached to 

 the females. No spiculae. 



Thus, then, we see that Gordius and Mermis differ very materially 

 from one another, while Sphaerularia departs even more from the com- 

 mon type, and indeed agrees with the other two in little except the ab- 

 sence of an anus, and the very peculiar corpus adiposum. M. Schneider 

 is therefore, no doubt, right in proposing to divide the Gordiaceae into 

 two families, to which we must now add a third — Sphaerulariaceae, for 

 the genus Sphaerularia. For the present we must leave the characters 



