418 Prof. R. Leuckart on the Developmental 
The formation of these organs is commenced by the paren- 
chyma of the body in the periphery of the anus separating from 
the chitinous envelopes and gradually removing further from it. 
In this way a dome-shaped cavity 1s produced in the interior of 
the caudal extremity, its axis being traversed by the lobately 
projecting rectum. Of course, the dome is not perfectly sym- 
metrical, but is obliquely truncated at its lower extremity in 
correspondence with the structure of the tail, with a shorter 
ventral and a longer dorsal lateral margin. 
As soon as the walls of the dome have been enlarged so 
as to produce a certain amount of surface, their parenchyma 
begins to undergo unequal division in a definite manner. There 
are produced numerous radiating blastema-streaks, which are 
united to each other by a more lamellar diffusion,—in other 
words, the ribs of the caudal hood, with their unitmg mem- 
branes, structures which consequently correspond morphologi- 
cally with the previous caudal extremity, and no doubt have the 
same origin essentially also in Dochmius and the other Strongy- 
lide. 
But during the formation and development of the caudal hood 
a peculiar transformation has also taken place at the anterior 
extremity of our worm, the future buccal cup having presented 
its first traces here, especially in the periphery of the anterior 
extremity of the cesophagus. The developmental history of this 
apparatus agrees in its essential particulars with the processes 
already described in Cucullanus, except that, in consequence of 
the much larger size of the worm, they are much more striking 
and may be more distinctly traced. To this may be added the 
circumstance that the buccal cup of Sclerostomum is composed 
of several (four) different portions, lying one behind the other 
like segments, so that it has a more complicated structure than 
in Cucullanus. Of course this circumstance has an influence on 
the development. It would, however, lead me too far if I were 
to attempt a detailed description of the different developmental 
processes ; consequently I shall only remark that the segments 
of the buccal cup very early rise like so many terraces on the 
inner wall of the new buccal cavity. As this takes place at a 
period when the cesophagus is still situated close behind the 
buccal rosette, it follows that at their first appearance these 
rings occupy precisely a reversed position; that is to say, the 
finally last segment is at first the foremost one. A change of 
position commences only at the retrogression of the cesophagus, 
which gradually brings the buccal cup to its definitive structure. 
The first embryonic form of Sclerostomum equinum is still 
unknown to me; but I can hardly doubt that it is essentially 
constructed as in Dochmius, and also leads the same life. Iam 
